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ASME B1.20.1-2013[Revision of ASME B1.20.1-1983 (R2006)]

Pipe Threads, General Purpose (Inch)

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ASME B1.20.1-2013[Revision of ASME B1.20.1-1983 (R2006)]

Pipe Threads,General Purpose(Inch)

A N A M E R I C A N N A T I O N A L S T A N D A R D

Two Park Avenue • New York, NY • 10016 USA



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Date of Issuance: November 15, 2013

This Standard will be revised when the Society approves the issuance of a new edition. There willbe no written interpretations of the requirements of this Standard issued to this edition.

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The American Society of Mechanical EngineersTwo Park Avenue, New York, NY 10016-5990

Copyright © 2013 byTHE AMERICAN SOCIETY OF MECHANICAL ENGINEERS

All rights reservedPrinted in U.S.A.



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CONTENTS

Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ivCommittee Roster . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vCorrespondence With the B1 Committee . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2 American National Standard Pipe Thread Form . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

3 Specification for Taper Pipe Threads, NPT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

4 Specifications for Internal Straight Threads in Pipe Couplings, NPSC . . . . . . . . . . . . . . . . . . 13

5 Specifications for Railing Joint Taper Pipe Threads, NPTR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

6 Specifications for Straight Pipe Threads for Mechanical Joints; NPSM, NPSL . . . . . . . . . . . 16

7 Gages and Gage Tolerances for American National Standard Taper PipeThreads, NPT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Figures1 Root, Crest, and Flank Engagement, NPT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Basic Form of American National Standard Taper Pipe Thread, NPT . . . . . . . . . . . . . . . 33 American National Standard Taper Pipe Thread Notation . . . . . . . . . . . . . . . . . . . . . . . . . . 64 Gaging External Taper Threads With L1 Ring Gage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 Gaging of Chamfered Threads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 Gaging Internal Taper Threads With L1 Plug Gage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 NPT Standard Taper Pipe Thread Plug and Ring Gages . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208 Suggested Form of Gage Thread . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Tables1 Limits on Crest and Root Truncation of American National Standard External

and Internal Taper Pipe Threads, NPT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 Basic Dimensions of American National Standard Taper Pipe Thread, NPT . . . . . . . . . 83 Tolerances on Taper, Lead, and Angle of Pipe Threads, NPT . . . . . . . . . . . . . . . . . . . . . . . 104 Dimensions, Internal Straight Threads in Pipe Coupling, NPSC . . . . . . . . . . . . . . . . . . . . 145 Dimensions of External and Internal Taper Pipe Threads for Railing

Joints, NPTR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156 Dimensions of External and Internal Straight Pipe Threads for Fixtures, NPSM . . . . . 177 Dimensions, External and Internal Straight Pipe Thread for Locknut

Connections, NPSL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188 Basic Dimensions of Threaded Gages for American National Standard Taper Pipe

Threads, NPT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229 Working Gage Tolerances for American National Standard Taper Pipe

Thread, NPT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2310 Diameter Equivalent of Variation in Half Included Angle of Thread for Tools

and Gages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2511 Diameter Equivalent of Variation in Lead for Tools and Gages . . . . . . . . . . . . . . . . . . . . . 26

Nonmandatory AppendicesA The Turns of Engagement Method of Gaging Product Threads . . . . . . . . . . . . . . . . . . . . . 27B Tap Drill Sizes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28C Thread Types and Corresponding Gages and Gaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

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FOREWORD

In 1973, American National Standards Committee B2, which had formerly been responsible forpipe thread standards, was absorbed by American National Standards Institute (ANSI) StandardsCommittee B1 and reorganized as Subcommittee 20. A complete rewrite of the B2.1-1968 standardon Pipe Threads (Except Dryseal) was undertaken. It was approved and formally designated asan American National Standard on February 4, 1983 and was reaffirmed in 2001 and 2006. Thesystem of numbering, to include metric conversions, is as follows:

ANSI/ASME B1.20.1, Pipe Threads, General Purpose (Inch)ASME B1.20.2M-2006, Pipe Threads, 60°, General Purpose (Metric Translation)These standards, ANSI/ASME B1.20.1 and B1.20.2M, have product thread dimensions and

gaging in the same document. Thread inspection specifies the use of L1 taper thread gages similarto B2.l-1968. In addition, emphasis was given to the requirement that all basic thread designdimensions were to be met within the specified tolerances.

This revision of ANSI/ASME B1.20.1 has both significant and subtle substantive changes tothe 1983 revision. It is more explanatory for the user than the previous revision. Significantchanges are as follows:

(a) An acceptability section has been added, providing a referee method in cases of dispute.This acknowledges the potentially wide but acceptable variation in the prescribed gages andgaging methods.

(b) Figures have been updated with additional information and drawn to be more visuallyexplanatory.

(c) The Turns of Engagement method has been moved to an appendix, due to its inherent gagecorrelation issues. This gaging method may be used when parties agree, but it is no longer anaccepted method within the Standard.

(d) Calculated data have been revised following the rounding rules of B1.30M. This providesa standardized high level of precision in calculation. Some tabulated values changed, but nochanges were deemed significant enough to affect the conformance status of products or gages.These changes are generally beyond the margin of error of the required measurements. NPTR,NPSM, and NPSL thread dimensions were not recalculated as some historical methodology,necessary for computation, was not available.

(e) Guidance for tap drill sizes has been updated to reflect varying manufacturing conditionsand the wider range of available drill sizes. Instead of specifying drill sizes, the Standard nowrefers to the tabulated basic minor diameter of the internal thread as a reference in which to basedrill size choice.

(f) Added are detailed explanations on the effects of coatings on threads, as well as guidancefor precoating size compensation.

(g) The gaging point of reference is moved for external threads having chamfer diameterssmaller than the minor diameter at the small end. This change was made to help ensure adequatethread engagement over a wider range of product thread chamfers. This change is correspondentto the existing treatment of chamfers for internal threads.

(h) The point of reference for checking wear on working gages is changed to basic. Previously,the point of reference was the size at the time of manufacture. This change facilitates the calibrationof gages when the original size at manufacture is not known and standardizes gage sizes atmaximum wear.

(i) Gaging guidance for straight pipe threads has been expanded, including allowing the No-Go to enter up to three turns, mimicking ASME B1.2.

(j) The use of indicating gages has been added as a gaging method.Following the approvals of the Standards Committee and ASME, approval for the new edition

was granted by ANSI on October 15, 2013.All requests for interpretation or suggestions for revisions should be sent to the Secretary,

B1 Committee, The American Society of Mechanical Engineers, Two Park Avenue, New York,NY 10016-5990.

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ASME B1 COMMITTEEStandardization and Unification of Screw Threads

(The following is the roster of the Committee at the time of approval of this Standard.)

STANDARDS COMMITTEE OFFICERS

A. L. Barrows, ChairD. S. George, Vice ChairA. L. Guzman, Secretary

STANDARDS COMMITTEE PERSONNEL

A. L. Barrows, Swanson Tool Manufacturing, Inc.K. Bly, Vermont Thread GageG. A. Cuccio, Capitol Manufacturing Co.R. Dodge, Pennoyer Dodge Co.D. Everrett, National Institute of Standards & TechnologyJ. O. Gehret III, Vermont Thread Gage, LLCD. S. George, Ramco SpecialtiesJ. Gervasi, Kerr Lakeside, Inc.J. Greenslade, Industrial Fastener InstituteA. L. Guzman, The American Society of Mechanical EngineersR. J. Hukari, SPS TechnologiesL. C. Johnson, The Johnson Gage Co.P. A. Larouche, Alternate, The Johnson Gage Co.D. D. Katz, Precision Fittings

SUBCOMMITTEE 20 — PIPE THREADS

D. D. Katz, Chair, Precision FittingsP. A. Larouche, Vice Chair, The Johnson Gage Co.K. Bly, Vermont Thread GageM. Cox, Contributing Member, ConsultantG. A. Cuccio, Capitol Manufacturing Co.R. Dodge, Pennoyer Dodge Co.J. O. Gehret III, Vermont Thread Gage, LLCJ. R. Gervasi, Kerr Lakeside, Inc.J. A. Gruber, Contributing Member, J. A. Gruber & Associates, LLCL. C. Johnson, The Johnson Gage Co.R. P. Knittel, Leitech-U.S. Ltd.

v

R. P. Knittel, Leitech-U.S. Ltd.M. H. McWilliams, PMC Lone StarD. R. Maisch, Alternate, PMC Lone StarD. Miskinis, Kennametal, Inc.D. R. Oas, Seaway Bolt & Specials Corp.J. R. Popovic, Cleveland Speciality Inspection Services, Inc.M. W. Rose, Glastonbury Southern GageE. Schwartz, ConsultantB. F. Sheffler, Dresser-Rand Co.D. Skierski, Contributing Member, Sterling Gage & Calibration, LLCR. D. Strong, Doerken Corp.A. F. Thibodeau, Honorary Member, Swanson Tool Manufacturing,

Inc.C. J. Wilson, Contributing Member, Consultant

X. Li, Contributing Member, China Productivity Center forMachinery Industry

D. R. Maisch, PMC Lone StarM. H. McWilliams, PMC Lone StarD. R. Oas, Seaway Bolt & Specials Corp.J. R. Popovic, Cleveland Speciality Inspection Services, Inc.M. W. Rose, Glastonbury Southern GageA. D. Shepherd, Emuge Corp.D. Skierski, Contributing Member, Sterling Gage & Calibration, LLCA. F. Thibodeau, Contributing Member, Swanson Tool

Manufacturing, Inc.



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CORRESPONDENCE WITH THE B1 COMMITTEE

General. ASME Standards are developed and maintained with the intent to represent theconsensus of concerned interests. As such, users of this Standard may interact with the Committeeby requesting interpretations, proposing revisions, and attending Committee meetings. Corre-spondence should be addressed to:

Secretary, B1 Standards CommitteeThe American Society of Mechanical EngineersTwo Park AvenueNew York, NY 10016-5990

Proposing Revisions. Revisions are made periodically to the Standard to incorporate changesthat appear necessary or desirable, as demonstrated by the experience gained from the applicationof the Standard. Approved revisions will be published periodically.

The Committee welcomes proposals for revisions to this Standard. Such proposals should beas specific as possible, citing the paragraph number(s), the proposed wording, and a detaileddescription of the reasons for the proposal, including any pertinent documentation.

Proposing a Case. Cases may be issued for the purpose of providing alternative rules whenjustified, to permit early implementation of an approved revision when the need is urgent, or toprovide rules not covered by existing provisions. Cases are effective immediately upon ASMEapproval and shall be posted on the ASME Committee Web page.

Request for Cases shall provide a Statement of Need and Background Information. The requestshould identify the Standard, the paragraph, figure or table number(s), and be written as aQuestion and Reply in the same format as existing Cases. Request for Cases should also indicatethe applicable edition(s) of the Standard to which the proposed Case applies.

Attending Committee Meetings. The B1 Standards Committee regularly holds meetings, whichare open to the public. Persons wishing to attend any meeting should contact the Secretary ofthe B1 Standards Committee.

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ASME B1.20.1-2013

Pipe Threads, General Purpose (Inch)

1 INTRODUCTION

1.1 Scope

This Standard covers dimensions and gaging of pipethreads of the following series:

NPTNPSCNPTRNPSMNPSL

1.2 Related Standard

Hose coupling joints are ordinarily made with straightinternal and external loose-fitting threads. There are sev-eral standards of hose threads having various diametersand pitches, one of which is based on the AmericanNational Standard Pipe Thread. By the use of this threadseries, NPSH, it is possible to join small hose couplingsin sizes 1⁄2 to 4, inclusive, to ends of standard pipe havingAmerican National Standard external pipe threads,using a gasket to seal the joint. For dimensions, toler-ances, and gaging, see ASME B1.20.7.

1.3 Thread Designations

1.3.1 The types of pipe threads included in thisStandard are designated by specifying in sequence thenominal pipe size, number of threads per inch, and thethread series symbol as follows:

1⁄8–27 NPT1⁄8–27 NPSC1⁄2–14 NPTR1⁄8–27 NPSM1⁄8–27 NPSLDecimal equivalent notation may be substituted for

fractional pipe sizes. For example

0.125–27 NPT

For left-hand threads, add “LH” to the designation.For example

1⁄8–27 NPT–LH

Designations without “LH” will signify right-handthreads.

1.3.2 Each of these letters in the symbols has signif-icance as follows:

N p National (American) Standard

1

P p PipeT p TaperS p StraightC p CouplingR p Railing Fittings

M p MechanicalL p Locknut

1.4 Sealing (NPT and NPSC Only)

1.4.1 Mating Threads. Mating threads shouldalways contact on the thread flanks. The design toler-ances are such that mating crests and roots may clear,contact, or interfere (see Fig. 1). This joint may not neces-sarily seal, unless a sealant is used.

1.4.2 Sealant. Where pressure-tight, leak-free jointsare required, it is intended that threads conforming tothis Standard be made up wrench-tight with a sealant.To prevent galling during installation, the sealant mayhave lubricating properties.

1.4.3 Tightening Torque. Due to application-specificvariables such as materials, wall thickness, operatingpressures, etc., no guidance is given in this Standardregarding joint-tightening torque. However, jointsshould be tightened beyond the hand-tight engagementposition. Advancing the joint past hand-tight createsinterference between external and internal thread flanks,produces a seal (with the use of a sealant), and helpsprevent loosening of the joint. Overtightening may bedetrimental to the sealing function of the joint.

1.4.4 Other Considerations. Out-of-roundness ofmating parts can negatively affect their ability to sealwhen made up wrench tight. The product’s elasticityand ductility will also affect sealing.

1.4.5 Pressure-Tight Threads Without Sealant. Pipethreads designed for pressure-tight joints that may beused without sealing compounds (Dryseal Threads) arecovered in ASME B1.20.3.

1.5 Appendices

Useful and supplementary information that is not apart of this Standard is presented in a nonmandatoryappendix. Specifically, the nonmandatory appendicescover the turns of engagement method of gaging, sug-gested prethreading hole diameters, and an explanatorygaging matrix.



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ASME B1.20.1-2013

Fig. 1 Root, Crest, and Flank Engagement, NPT

External Thread

Internal Thread

Roots and crests clear

Roots and crests contact

Roots and crests interfere

1.6 Referenced Standards

The latest issues of the following documents form apart of this Standard to the extent specified herein.

ASME B1.2, Gages and Gaging for Unified ScrewThreads

ASME B1.7, Screw Threads: Nomenclature, Definitions,and Letter Symbols

ASME B1.20.3, Dryseal Pipe Threads (Inch)ASME B1.20.7, Hose Coupling Screw Threads (Inch)ASME B1.30, Screw Threads: Standard Practice for

Calculating and Rounding DimensionsASME B47.1, Gage Blanks

Publisher: The American Society of MechanicalEngineers (ASME), Two Park Avenue, New York, NY10016-5990; Order Department: 22 Law Drive, P.O.Box 2900, Fairfield, NJ 07007-2900 (www.asme.org)

1.7 Terminology

Definitions of terms and symbols for thread dimen-sions are given in ASME B1.7.

2

2 AMERICAN NATIONAL STANDARD PIPE THREADFORM

2.1 Thread Form

The form of thread profile specified in this Standardshall be known as the American National Standard PipeThread Form (see Fig. 2).

2.2 Angle of Thread

The angle between the sides of the thread is 60 degwhen measured in an axial plane. The line bisecting thisangle is perpendicular to the axis.

2.3 Thread Height

The height of the sharp V thread, H, is

H p 0.86602540P

where

P p pitch of thread



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ASME B1.20.1-2013

Fig. 2 Basic Form of American National Standard Taper Pipe Thread, NPT

External Thread Internal Thread

Axis

90 deg 90 deg

60 deg

90 deg 90 deg

Crest

Root

Frs

frsh

H

Fcs

fcs

fcn

Fcn

Crest

RootP

frn

Frn

90 deg

3



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ASME B1.20.1-2013

For a symmetrical straight screw thread with a 30-degflank angle, H p cot �/2n p 0.86602540P. For a symmet-rical taper screw thread with a 30-deg flank angle anddiametral taper of 0.750 in./ft, H p (cot � − tan2 � tan�)/2n p 0.86574320P. For an 8-pitch thread, which isthe coarsest standard taper pipe thread pitch, the corres-ponding values of H are 0.1082179 and 0.1082532, respec-tively. The difference of 0.000035 in. being insignificant,the value of H p 0.86602540P is used for all straightand tapered threads in this Standard.

2.4 Thread Truncation

The maximum height of the truncated thread, h (seeFig. 2), is based on factors entering into the manufactureof cutting tools and the making of tight joints.

h p 0.800P

The crest and root of pipe threads are truncated aminimum of 0.033P. The maximum depth of truncationfor the crest and root of these pipe threads will be foundin Table 1. The crests and roots of the external and inter-nal threads may be truncated either parallel to the pitchline or parallel to the axis. The illustration in Table 1,giving a sectional view of this Standard thread form,represents the truncated thread form by a straight lineand sharp corners. However, a radius form is acceptable,as long as the crests and roots lie within the limits shownin Table 1. Some of the truncations in this illustrationare shown with dotted lines as radii.

3 SPECIFICATION FOR TAPER PIPE THREADS, NPT

3.1 General

NPT joints made in accordance with these specifica-tions consist of an external taper and internal taperthread (see Figs. 1 through 3). NPT taper pipe threadsare intended to be made up wrench-tight and with asealant when a pressure-tight joint is required.

3.1.1 Notation. The standard notation applicableto the American National Standard Taper Pipe Thread,NPT, is shown in Fig. 3.

3.1.2 Symbols. The following symbols are specificto this Standard:

D p outside diameter of pipeE0 p basic pitch diameter at small end of external

thread (or end of pipe)E1 p basic pitch diameter at plane of hand-tight

engagement length (L1), external thread, andlarge end of internal thread

E2 p basic pitch diameter at plane of effectivethread length (L2), external thread

E3 p basic pitch diameter at plane of wrench-tightengagement

E5 p basic pitch diameter pipe at L5, plane of com-plete thread length

4

K0 p basic minor diameter at small end of externalthread (or end of pipe)

L1 p length of hand-tight engagement betweeninternal and external threads

L2 p length of effective thread, external thread.Equal to L1 plus wrench make-up threads

L3 p length of thread beyond L1 allowing wrench-tight engagement, internal thread (also,wrench make-up)

L4 p overall length of thread, including vanishthread, external thread

L5 p length of complete threads, external thread,where cone of major diameter intersects out-side diameter of pipe

V p length of vanish threads

3.1.3 Handling Considerations. The potential effectson thread form and gaging must be considered whenchoosing coatings and other processes. Some processes,such as barrel coating, can be damaging to the threadform, especially the crests of external threads. See para.3.2.3 on gaging nicked threads.

3.1.4 Form of Thread. The form of the thread isspecified in para. 2.1.

3.1.5 Taper of Thread. The basic taper of the threadis 1 in 16 or 0.75 in./ft measured diametrically relativeto the axis.

3.1.6 Pitch Diameters of Thread. The basic pitchdiameters of the tapered thread are determined by thefollowing formulas based on the outside diameter of thepipe and the pitch of the thread:

E0 p D − (0.05D + 1.1) 1/np D − (0.05D + 1.1)P

E1 p E0 + 0.0625 L1

whereD p outside diameter of pipeE0 p pitch diameter of thread at end of pipe or

small end of external threadE1 p pitch diameter of thread at the large end of

internal threadL1 p hand-tight length of engagement between

external and internal threads, also the hand-tight length of thread for both internal andexternal threads

n p threads per inch

3.1.7 Length of Effective Thread. The basic lengthof the effective external taper thread L2, is determinedby the following formula based on the outside diameterof the pipe and the pitch of the thread:

L2 p (0.80D + 6.8)1/np (0.80D + 6.8)P

whereD p outside diameter of pipen p threads per inch



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ASME B1.20.1-2013

Table 1 Limits on Crest and Root Truncation of American National Standard External andInternal Taper Pipe Threads, NPT

Minimum truncation

Maximum truncation

Minimum truncation

Maximum truncation

External Thread

Internal Thread

Root

Crest

Crest

Root

Crest

Minimum truncation

Maximum truncation

Minimum truncation

Maximum truncation

Max. h

H

Truncation, f Equivalent Width of Flat, FHeight of Thread,Height ofh Min. Max. Min. Max.Threads/ Sharp V

Inch, n Thread, H Min. Max. Formula in. Formula in. Tolerance Formula in. Formula in. Tolerance

1 2 3 4 5 6 7 8 9 10 11 12 13 14

27 0.0320750 0.02496 0.02963 0.033P 0.0012 0.096P 0.0036 0.0024 0.038P 0.0014 0.111P 0.0041 0.002718 0.0481125 0.03833 0.04444 0.033P 0.0018 0.088P 0.0049 0.0031 0.038P 0.0021 0.102P 0.0057 0.003614 0.0618590 0.05072 0.05714 0.033P 0.0024 0.078P 0.0056 0.0032 0.038P 0.0027 0.090P 0.0064 0.003711.5 0.0753066 0.06261 0.06957 0.033P 0.0029 0.073P 0.0063 0.0034 0.038P 0.0033 0.084P 0.0073 0.0040

8 0.1082532 0.09275 0.100 0.033P 0.0041 0.062P 0.0078 0.0037 0.038P 0.0048 0.072P 0.0090 0.0042

GENERAL NOTE: The basic dimensions of the American National Standard Taper Pipe Thread are given in inches to four or five decimal places.While this implies a greater degree of precision than is ordinarily attained, these dimensions are the basis of gage dimensions and are soexpressed for the purpose of eliminating errors in computations.

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ASME B1.20.1-2013

Fig. 3 American National Standard Taper Pipe Thread Notation

Pla

ne

of

wre

nch

mak

e-u

p

Ref

eren

ce p

lan

e

zero

Pla

ne

of

han

d-t

igh

t

eng

agem

ent

Pla

ne

of

com

ple

te

thre

ad le

ng

th

Pla

ne

of

effe

ctiv

e

Pla

ne

of

van

ish

po

int

thre

ad le

ng

th

Wrench make-up

L3 L1

L5

L2

L4

V

2P

E2 d DE5E1E0K0E3

6



--``,,,,`,`,,`,`````,`,,`,`,`-`-`,,`,,`,`,,`---

ASME B1.20.1-2013

This formula determines the length of effective exter-nal thread. This may include two usable threads incom-plete at the crest.

3.1.8 Hand-Tight Engagement Between External andInternal Taper Threads. The basic length of engagementbetween external and internal taper threads whenscrewed together hand-tight is L1, shown in column 6,Table 2.

3.1.9 Wrench-Tight Engagement Between Externaland Internal Taper Threads. The external thread length,L2 − L1, and the internal thread length, L3, are allowancesfor wrench-tight assembly after the hand-tight engage-ment of L1 lengths.

3.1.9.1 Thread Engagement Considerations. Thegaging tolerance of ±1 turn for both external and internalthreads has the effect of potentially increasing the lengthof engagement by up to two turns or reducing the lengthof engagement by up to two turns. Working gage wearhas the additional effect of reducing thread engagementby the amount gages wear past basic.

3.1.9.2 Special Applications. It is recognized thatin special applications, such as flanges for high-pressurework, longer thread engagement is needed, in whichcase the pitch diameter (dimension E1, Table 2) is main-tained and the pitch diameter E0 at the end of the pipeis made smaller. The taper must be kept at 3⁄4 in./ft, andthread is made longer.

3.1.10 Tolerances on Product Taper, Lead, andAngle. The permissible variations in taper, lead, andangle are given in Table 3. This table is a guide forestablishing limits of the thread elements of threadingtools. The correct manufacture of tools and the use ofgages should provide adequate control of functionalsize.

3.1.11 Basic Dimensions. The basic dimensions oftaper pipe threads, derived from the above specifica-tions, are given in Table 2.

3.2 Gaging NPT ThreadsThe L1 gages prescribed in this Standard are consid-

ered functional in that they give assurance of assembla-bility over the L1 length, the length of hand-tightengagement. They simulate a mating product thread thatconforms to this Standard. They encompass multipleelements of the thread, including thread diameters, flankangle, lead, taper, and root truncation. The simultaneousengagement of all elements results in a measurementthat reflects the cumulative variation of all those ele-ments, the functional diameter. This is expressed asstandoff for rings and plugs or measured directly byindicating gages. See section 7 for gage specifications.

3.2.1 External Thread Gaging

3.2.1.1 L1 Ring Gage. The L1 ring and externalproduct thread are screwed together hand-tight, and the

7

position relative to the small end of the ring (or basicstep on a stepped ring gage) is noted (see Figs. 4 and5). This is the standoff. The tolerance for the standoff is±1 turn (or ±1 pitch, as shown in column 4 of Table 2)from the small end of the ring (or basic step on astepped ring).

3.2.1.2 External L1-Indicating Gage. The externalL1-indicating gage is set with a master plug gage, whichis made to basic dimensions. Accordingly, when theproduct is engaged by an indicating gage, readings indi-cate the diametral variation from basic. The tolerancefrom basic is the diametral equivalent to ±1 pitch (or±0.0625/n, as shown in column 23 of Table 2).

3.2.2 Internal Thread Gaging

3.2.2.1 L1 Plug Gage. The L1 plug gage and inter-nal product thread are screwed together hand-tight, andthe position relative to the basic step of the gage is noted(see Figs. 5 and 6). This is the standoff. The tolerancefor the standoff is ±1 turn (or ±1 pitch, as shown incolumn 4 of Table 2) from the basic step of the plug gage.

3.2.2.2 Internal L1-Indicating Gage. The internalL1-indicating gage is set with a master ring gage, whichis made to basic dimensions. Accordingly, when theproduct is engaged by an indicating gage, readings indi-cate the diametral variation from basic. The tolerancefrom basic is the diametral equivalent to ±1 pitch (or±0.0625/n, as shown in column 23 of Table 2).

3.2.3 Nicked Threads. Pipe threads are particularlysusceptible to damage that interferes with proper gag-ing. Generally, this damage appears as “nicks” on thecrest of external or internal threads. These nicks willalways hold the gage back from properly seating. Thismakes the external functional size seem larger than itis and the internal functional size seem smaller than itis. Because pipe threads are designed to be installedwrench-tight, and the wrenching reforms the nicks totheir proper crest position, some degree of nicking isacceptable. A product mated with a gage may be“rapped” and hand-tightened while engaged. Careshould be exercised when rapping to minimize thepotential damage to the gage. Rapping and tighteningmay continue until the product and gage do not engageany further. Products that remain beyond the gagingtolerance after rapping and hand-tightening arenonconforming.

3.2.4 Treatment of Chamfers, Recesses,Counterbores. Threaded products have thread cham-fers to avoid sharp edges, protect the start thread, andaid in assembly. The nature of threads generally necessi-tates external chamfer diameters at least as small as theminor diameter and internal chamfer diameters at leastas large as the major diameter, if complete sharp edgeremoval is desired. In practice, many product threadchamfers exceed the minimal chamfer that removes the



--``,,,,`,`,,`,`````,`,,`,`,`-`-`,,`,,`,`,,`---

ASME B1.20.1-2013

Tabl

e2

Bas

icD

imen

sion

sof

Amer

ican

Nat

iona

lSt

anda

rdTa

per

Pipe

Thre

ad,

NPT

L 4

V

2P

E2

DE

5E

1E

0K

0E

3

L 2

L 5

L 3L 1

Van

ish

th

read

s d

ue

to c

ham

fer

on

die

Tap

er o

f th

read

1 in

16

mea

sure

d o

n d

iam

eter

8



--``,,,,`,`,,`,`````,`,,`,`,`-`-`,,`,,`,`,,`---

ASME B1.20.1-2013

Tabl

e2

Bas

icD

imen

sion

sof

Amer

ican

Nat

iona

lSt

anda

rdTa

per

Pipe

Thre

ad,

NPT

(Con

t’d)

Basi

cPi

tch

Chan

geM

inor

6

Leng

th,L

1Di

amet

erin

Diam

eter

Hand

-tigh

tEf

fect

ive

Thre

ad,

Plan

eto

L 2No

min

alCo

mpl

ete

atDi

amet

erat

Wre

nch

Mak

e-Up

Leng

th,

Enga

gem

ent

Exte

rnal

Plan

e,Ex

tern

alTh

read

s5

Begi

nnin

gO

vera

llpe

rSm

all

Inte

rnal

Thre

adEx

tern

alVa

nish

O.D.

Pitc

hof

Pitc

hPi

tch

Leng

th,

Pitc

hHe

ight

Turn

End

Leng

th,1

Leng

th,3

Thre

ad,

Leng

th,

Thre

ad,

Leng

th,

Nom

inal

ofof

Exte

rnal

Diam

-Di

am-

Pitc

hEx

tern

alDi

am-

ofof

ofL 1

L 2L 2

−L 1

L 3V

L 5Pi

pePi

pe,

Thre

ads/

Thre

ad,

Thre

ad,

eter

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er,

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-Th

read

,4et

er,

Thre

ad,

Thre

ad,

Pipe

,Si

zeD

Inch

,nP

E 0in

.Th

read

sE 1

in.

Thre

ads

E 3in

.Th

read

sin

.Th

read

set

er,E

3in

.Th

read

sL 4

in.

E 5h

0.06

25/n

K o

12

34

56

78

910

1112

1314

1516

1718

1920

2122

2324

1 ⁄ 160.

3125

270.

0370

3704

0.27

118

0.16

004.

320.

2811

80.

2611

7.05

0.28

750

0.10

112.

730.

1111

30.

2642

40.

1285

3.47

0.38

960.

1870

0.28

287

0.02

963

0.00

231

0.24

151 ⁄ 8

0.40

5027

0.03

7037

040.

3635

10.

1615

4.36

0.37

360

0.26

397.

130.

3800

00.

1024

2.76

0.11

113

0.35

656

0.12

853.

470.

3924

0.18

980.

3753

70.

0296

30.

0023

10.

3338

1 ⁄ 40.

5400

180.

0555

5556

0.47

739

0.22

784.

100.

4916

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4018

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0.50

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0.17

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130.

1667

30.

4669

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1928

3.47

0.59

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2907

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340.

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673

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160

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470.

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0444

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5675

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2857

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7784

30.

5337

7.47

0.79

178

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2143

30.

7450

40.

2479

3.47

0.78

150.

3909

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286

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14

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1.31

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1.21

363

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601.

2386

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6828

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0.28

283.

250.

2609

31.

1973

30.

3017

3.47

0.98

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5089

1.24

544

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957

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543

1.14

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1.66

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5833

80.

7068

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490.

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31.

7797

80.

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5496

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5826

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3.32

500

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471.

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003.

4000

00.

1000

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13.

2406

31 ⁄ 24.

0000

80.

1250

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3.83

750

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106.

573.

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124

GEN

ERA

LN

OTE

:Th

eba

sic

dim

ensi

ons

ofth

eA

mer

ican

Nat

iona

lS

tand

ard

Tape

rPi

peTh

read

are

give

nin

inch

esto

four

orfiv

ede

cim

alpl

aces

.W

hile

this

impl

ies

agr

eate

rde

gree

ofpr

ecis

ion

than

isor

dina

rily

atta

ined

,th

ese

dim

ensi

ons

are

the

basi

sof

gage

dim

ensi

ons

and

are

soex

pres

sed

for

the

purp

ose

ofel

imin

atin

ger

rors

inco

mpu

tati

ons.

NO

TES

:(1

)A

lso

leng

thof

L 1ri

ngga

gean

dle

ngth

from

gagi

ngno

tch

tosm

all

end

ofL 1

plug

gage

.(2

)A

lso

pitc

hdi

amet

erat

gagi

ngno

tch

ofL 1

plug

gage

(han

d-ti

ght

plan

e).

(3)

Als

oth

read

edle

ngth

ofL 1

plug

gage

.(4

)Re

fere

nce

dim

ensi

on.

(5)

The

leng

thL 5

from

the

end

ofth

epi

pede

term

ines

the

plan

ebe

yond

whi

chth

eth

read

form

isin

com

plet

eat

the

cres

t.Th

ene

xttw

oth

read

sar

eco

mpl

ete

atth

ero

ot.

At

this

plan

e,th

eco

nefo

rmed

byth

ecr

ests

ofth

eth

read

inte

rsec

tsth

ecy

linde

rfo

rmin

gth

eex

tern

alsu

rfac

eof

the

pipe

(L5

pL 2

−2P

).(6

)G

iven

asin

form

atio

nfo

rus

ein

sele

ctin

gta

pdr

ills

(see

Non

man

dato

ryA

ppen

dix

B).

9



--``,,,,`,`,,`,`````,`,,`,`,`-`-`,,`,,`,`,,`---

ASME B1.20.1-2013

Table 3 Tolerances on Taper, Lead, and Angle of Pipe Threads, NPT

Tolerances

Taper on Pitch Line,3⁄4 in./ftThreads/ Lead in Effective 60-deg Angle of

Nominal Pipe Size Inch, n Max. Min. Length of Threads Threads, Deg

1 2 3 4 5 6

1⁄16, 1⁄8 27 +1⁄8 −1⁄16 ±0.003 ±21⁄21⁄4, 3⁄8 18 +1⁄8 −1⁄16 ±0.003 ±21⁄2, 3⁄4 14 +1⁄8 −1⁄16 ±0.003 ±2

1, 11⁄4, 11⁄2, 2 11.5 +1⁄8 −1⁄16 ±0.003 ±11⁄221⁄2 and larger 8 +1⁄8 −1⁄16 ±0.003 [Note (1)] ±11⁄2

NOTE:(1) The tolerance on lead shall be ±0.003 in./in. on any size threaded to an effective thread length greater than 1 in.

Fig. 4 Gaging External Taper Threads With L1 Ring Gage

(a) Basic Size (b) Maximum Size (c) Minimum Size

Ring gage Ring gage Ring gage

Flush One turn large

One turn small

10



--``,,,,`,`,,`,`````,`,,`,`,`-`-`,,`,,`,`,,`---

ASME B1.20.1-2013

Fig. 5 Gaging of Chamfered Threads

Chamfered Internal Thread

of Basic Size With Chamfer

Exceeding the Major Diameter

Chamfered External Thread


Diameter Smaller Than

the Minor Diameter

Chamfered External Thread of

Basic Size With the Chamfer

Diameter the Same as

the Minor Diameter

Chamfered Internal Thread


Diameter the Same as the

Major Diameter

Ring gage

Ring gage

Pipe or fitting

Pipe or fitting

Gaging face

Point of last thread scratch

Gaging face


Fitting

Plug gage

Fitting

Plug gage



Plane of gaging notch

Plane of gaging notch

(c)

(a) (b)

(d)

GENERAL NOTE: See para. 3.2.4.

11



--``,,,,`,`,,`,`````,`,,`,`,`-`-`,,`,,`,`,,`---

ASME B1.20.1-2013

Fig. 6 Gaging Internal Taper Threads With L1 Plug Gage

(a) Basic Size (b) Maximum Size (c) Minimum Size

Plug gage

Plug gage

Plug gage

Flush One turn large One turn small

sharp edge to better ensure sharp edge removal. Theexistence of chamfers has the effect of reducing engagedthread length, and larger chamfers further reduce threadlength. Designers and manufacturers are therefore cau-tioned to take into consideration the effects of chamferson the intended assembly. The gaging reference pointfor a product thread depends on the chamfer diameter.

3.2.4.1 For an external thread with a chamferdiameter smaller than the minor diameter, the referencepoint is the last scratch of the chamfer cone [see Fig. 5,illustration (a)].

3.2.4.2 For an internal thread with a chamferdiameter larger than the major diameter, the referencepoint is the last scratch of the chamfer cone [see Fig. 5,illustration (b)].

3.2.4.3 For an external thread with a chamferdiameter equal to or greater than the minor diameter,the reference point is the end of the fitting [or pipe; seeFig. 5, illustration (c)].

3.2.4.4 For an internal thread with a chamferdiameter equal to or smaller than the major diameter,the reference point is the end of the fitting [see Fig. 5,illustration (d)].

3.2.4.5 Recesses and counterbores must beaccounted for when gaging internal threads. Dogpointsor lead-ins to external threads must be accounted for

12

when gaging external threads. These features must notbe included in thread length measurements.

3.2.5 Acceptance of Product Made Prior to This Revi-sion. This revision includes changes to gaging practice,specifically the changing of the gaging point of referencefor external threads having chamfer diameters smallerthan the minor diameter at the small end. This changeis an important advance and should be implementedupon issuance of this Standard. As long as there are nospecifically identified assembly issues, products con-forming to the prior revision of this document are con-sidered suitable and allowed for sale and acceptanceuntil depleted.

3.2.6 Coated Threads. The specifications in thisStandard do not include an allowance for coating (orplating). If coating is desired, it may be necessary tomodify the threads since the gaging requirements mustbe satisfied for coated and uncoated parts. This may beemphasized by adding the words “AFTER COATING”to the thread designation of the finished product. Gagelimits before coating may be specified, followed by thewords “BEFORE COATING” or “PRE-PLATE.”

3.2.6.1 Coating Buildup. If significant, a coatingbuildup will necessitate making external threads smallerand internal threads larger, so that after coating, threadsizes and gaging are conforming to the Standard. It isimportant to note that coating buildup on the flanks of



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ASME B1.20.1-2013

threads increases external thread pitch diameter sizesand reduces internal pitch diameter sizes by four timesthe coating thickness. Coating buildup in crests androots increases major diameter sizes and decreasesminor diameter sizes by two times the coating thickness.See paras. 3.2.6.2 and 3.2.6.3 for guidance on compensat-ing for uniform coatings. Many product coatings do notcoat features evenly. Information about coating buildupshould be obtained from the coating processor.

3.2.6.2 Precoating Gaging Standoff Compensation,Internal Thread. Thread gaging standoff tolerance maybe adjusted to compensate for a uniform coating withan upper and lower thickness tolerance in the followingmanner:EXAMPLE: 1⁄2–14 NPT internal thread with uniform coatingthickness of 0.0002 in. to 0.0004 in. After coating, final producttolerance is flush ±1 turn standoff. Before coating, tolerance isestablished by the following formula:

Large end of product tolerance:1 turn large + (minimum coating thickness � 60-deg thread

constant � taper standoff constant)or0.0714 in. large + (0.0002 in. � 4 � 16) p 0.0842 in. large

Small end of product tolerance:1 turn small − (maximum coating thickness � 60-deg thread

constant � taper standoff constant)or0.0714 in. small − (0.0004 in. � 4 � 16) p 0.0458 in. small

Calculated before coating standoff tolerance: 0.0842 in. large to0.0458 in. small.

Threads with nonuniform coatings or other residualeffects (like nicks) may have to be compensated for dif-ferently to obtain standard after-coating tolerances.

3.2.6.3 Precoating Gaging Standoff Compensation,External Thread. Thread gaging standoff tolerance maybe adjusted to compensate for a uniform coating withan upper and lower thickness tolerance in the followingmanner:EXAMPLE: 1⁄2–14 NPT external thread with uniform coatingthickness of 0.0002 in. to 0.0004 in. After coating, final producttolerance is flush ±1 turn standoff. Before coating, tolerance isestablished by the following formula:

Small end of tolerance:1 turn small + (minimum coating thickness � 60-deg thread

constant � taper standoff constant)or0.0714 in. small + (0.0002 in. � 4 � 16) p 0.0842 in. small

Large end of tolerance:1 turn large − (maximum coating thickness � 60-deg thread

constant � taper standoff constant)or0.0714 in. large − (0.0004 in. � 4 � 16) p 0.0458 in. large

Calculated before coating standoff tolerance: 0.0842 in. small to0.0458 in. large.

13

Threads with nonuniform coatings or other residualeffects (like nicks) may have to be compensated for dif-ferently to obtain standard after-coating tolerances.

3.2.6.4 Precoating Gages. Special modified ringand plug gages may be designed and used in place ofthe standoff compensation methods described above.These are based on the standard gages described insection 7. It is common to modify the gage diameterssuch that the plug’s basic step and the small end ofthe ring are flush with product threads that are at acompensated basic size. Formulas similar to those abovemay be used in arriving at modified gage sizes.

3.2.7 Supplemental Gaging Conformance to thisStandard requires that all basic design dimensions bemet (within applicable tolerances), including taper,thread truncations, lead, and thread flank angle over theL2 and L3 lengths. Since the gaging systems prescribedin this Standard may not ensure conformance to theseindividual thread elements, supplemental gaging maybe employed to evaluate conformance. When supple-mental gaging is employed, it shall be agreed upon bythe supplier and purchaser. It is common to measuretruncation equivalent width of flat (Table 1) by opticalprojection of external threads directly to determinewhether or not such truncations are within the limitsspecified or particularly to see that maximum truncationis not exceeded.

3.3 Acceptability

Thread gages made to this Standard will have varia-tion between them due to gage manufacturing tolerancesand allowable gage wear. There can be more variationin tapered thread gaging than straight thread gaging dueto the interplay of the taper variations (within tolerance)between gages and products. The functional gagingrequirement of this Standard will be met when the prod-uct is accepted by a gage that conforms to this Standard.It is acknowledged that the allowable differences in con-forming gages may produce wider ranges of productdimensions than would be constructed strictly by thethread drawings and tolerances. However, product func-tionality and interchangeability are ultimately met usingthese gages.

4 SPECIFICATIONS FOR INTERNAL STRAIGHTTHREADS IN PIPE COUPLINGS, NPSC

4.1 Pressure-Tight Internal Straight Pipe Threads

Threads made in accordance with these specificationsare straight (parallel) threads of the same thread formas the American National Standard Taper Pipe Threadspecified in para. 2.1. They are used to form pressure-tight joints when assembled with an NPT external taperthread and made up wrench-tight with sealant (seepara. 1.4).



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ASME B1.20.1-2013

Table 4 Dimensions, Internal Straight Threads in Pipe Coupling, NPSC(Pressure-Tight Joints With Sealant)

Pitch Diameter [Note (1)]O.D. Pipe, Minimum MinorNominal Pipe Size D Threads/Inch, n Diameter Min. Max.

1 2 3 4 5 6

1⁄8 0.405 27 0.340 0.3701 0.37711⁄4 0.540 18 0.442 0.4864 0.49683⁄8 0.675 18 0.577 0.6218 0.63221⁄2 0.840 14 0.715 0.7717 0.78513⁄4 1.050 14 0.925 0.9822 0.99561 1.315 111⁄2 1.161 1.2305 1.2468

11⁄4 1.660 111⁄2 1.506 1.5752 1.591511⁄2 1.900 111⁄2 1.745 1.8142 1.8305

2 2.375 111⁄2 2.219 2.2881 2.304421⁄2 2.875 8 2.650 2.7504 2.7739

3 3.500 8 3.277 3.3768 3.400231⁄2 4.000 8 3.777 3.8771 3.9005

4 4.500 8 4.275 4.3754 4.3988

NOTE:(1) The actual pitch diameter of the straight tapped hole will be slightly smaller than the value given when gaged with a taper plug gage

as specified in para. 4.2.1.

4.1.1 Thread Designation. The American NationalStandard Coupling Straight Pipe Threads are designatedin accordance with para. 1.3.1 as follows:

1⁄8–27 NPSC

4.1.2 Dimensions and Limits of Size. The dimen-sions and pitch diameter limits of size are specified inTable 4. The pitch diameter sizes correspond to the gag-ing tolerance of one and one-half turns large or smallof the NPT E1. The major and minor diameters varywith the pitch diameter, as the American National Stan-dard Pipe Thread form is maintained within the trunca-tion tolerances shown in Table 1.

4.2 Gaging NPSC Internal Threads

Internal taper thread gages in accordance with section7 shall be used to gage NPSC straight internal pipethreads.

4.2.1 L1 Plug Gage. The L1 plug gage and internalproduct thread are screwed together hand-tight and theposition relative to the basic step of the gage is noted.This is the standoff. The NPSC tolerance for the standoffis ±11⁄2 turns (or ±11⁄2 pitch, as shown in column 4 ofTable 2) from the basic step of the plug gage. See paras.3.2.4.1 and 3.2.4.2 for chamfered threads.

4.2.2 L1 Internal Indicating Gage. When product isengaged in an indicating gage set with a master gage,readings indicate the diametral variation from basic. Thetolerance from basic is the diametral equivalent to ±11⁄2pitches (or ±0.0625/n, as shown in column 23 of Table 2).See paras. 3.2.4.1 and 3.2.4.2 for chamfered threads.

14

CAUTION: When using tapered thread gages in straight prod-uct threads, nonuniformity of gage wear is a particular problem;therefore, tapered gages used for this application should bechecked by direct measurement of thread form and size in addi-tion to checking against a master.

5 SPECIFICATIONS FOR RAILING JOINT TAPERPIPE THREADS, NPTR

5.1 Railing Joints

Railing joints that require a rigid mechanical taperthread joint may be made with external and internaltaper threads. The external thread is the same as theNPT thread, except that it is shortened to permit theuse of the larger end of the pipe thread. The internalthread has the same basic dimensions as the NPT inter-nal thread; however, a recess in the fitting provides acovering for the last scratch or sharp edges of incompletethreads on the pipe. The dimensions of these threadsare shown in Table 5.

5.1.1 Thread Designation. American National Stan-dard Railing Joint Taper Pipe Threads are designated inaccordance with para. 1.3.1 as follows:

1⁄2–14 NPTR

5.1.2 Form of Thread. The form of the thread is thesame as the American National Standard Taper PipeThread shown in Figs. 1 and 2.

5.2 Gaging and Tolerances, NPTR

The dimensions of these threads are specified in Table5. Gaging is performed using standard NPT L1 gages



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ASME B1.20.1-2013

Tabl

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Dim

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7).

15



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ASME B1.20.1-2013

(see section 7). Since the basic length and size (Table 5,column 5) of the external thread have been reducedsignificantly from standard NPT, the start end of theproduct thread will always lie inside the face of the gage.The maximum allowable variation in the external threadis no turns large and one turn small from this modi-fied basic.

EXAMPLE:For a 1⁄2–14 NPTR external thread, Table 5, column 7: the startend of the modified basic thread lies three threads inside theface of the gage. The tolerance during gaging will be 2 turnslarge to 3 turns large.For a 1⁄2–14 NPTR internal thread, Table 5, column 18: the startend of the modified basic thread lies four threads inside theface of the fitting. The tolerance during gaging will be 4 turnslarge to 5 turns large.

6 SPECIFICATIONS FOR STRAIGHT PIPE THREADSFOR MECHANICAL JOINTS; NPSM, NPSL

6.1 Straight Pipe Threads for Mechanical Joints

In addition to pressure-tight pipe joints, for whichtaper external threads and taper or straight internalthreads can be used, there are mechanical joints wherestraight pipe threads are used. Their pitch diametersand root and crest truncations vary as described below.These types of joints are as follows:

(a) free-fitting mechanical joints for fixtures, Table 6,both external and internal, NPSM

(b) loose-fitting mechanical joints with lock-nuts,Table 7, both external and internal, NPSL

6.1.1 Thread Designations. These threads are desig-nated in accordance with para. 1.3.1 as follows:

1⁄8–27 NPSM

1⁄8–27 NPSL

6.1.2 Pitch and Flank Angle. The pitch and flankangle are the same as the corresponding dimensions ofthe taper pipe thread described in section 3.

6.1.3 Diameter of Thread. The basic pitch diameterfor both the external and internal threads is equal to E1of Table 2, which is the same as the large end of theinternal NPT thread.

6.2 Free-Fitting Mechanical Joints for Fixtures, NPSM

Pipe is often used for special applications where thereare no internal pressures and, consequently, no sealingrequirements. Also, straight pipe threads are sometimesfound more suited or convenient where straight threadjoints are required for mechanical assemblies. In thesecases, NPSM threads can be used, creating a reasonablyclose fit of mating parts. The dimensions of these threadsare given in Table 6. Gaging is described in para. 6.4.

16

6.3 Loose-Fitting Mechanical Joints With Locknuts,NPSL

The American National Standard External LocknutThread is designed to produce a pipe thread having thelargest diameter that is possible to cut on standard pipe.Ordinarily, straight internal threads are used with thesestraight external threads, providing a loose fit. Thedimensions of these threads are given in Table 7. It will benoted that the maximum major diameter of the externalthread is slightly greater than the nominal outside diam-eter of the pipe. The normal manufacturer’s variationin pipe diameter provides for this increase. One applica-tion of a taper pipe thread in combination with a locknutthread that has been in use for some time is that shownin Table 7. It consists of the nipple threaded joint usedto connect standpipes with the floor or wall of a watersupply tank.

6.4 Gaging for NPSM and NPSL Threads

Gaging to properly control the production of thesestraight threads should be through the use of GO andNOT GO gages or indicating type gages.

6.4.1 GO Gaging. The GO size is acceptable whenthe GO thread gage (plug or ring) freely engages thefull threaded length of the product.

6.4.2 NOT GO Gaging. The NOT GO size is accept-able when the NOT GO thread gage (plug or ring)applied to the product thread does not enter more thanthree complete turns. The gage should not be forced.Special conditions, such as exceptionally thin or ductilematerial, small number of threads, etc., may necessitatemodification of this practice.

6.4.3 Indicating Gages. When using indicatinggages for straight threads, refer to ASME B1.2 for use.

6.4.4 Gage Dimensions. Gages used for NPSM shallbe made to the pitch diameter limits specified in Table 6.Gages used for NPSL shall be made to the pitch diameterlimits specified in Table 7. These gages shall be madein accordance with standard practice for straight threadgages as outlined in ASME B1.2. The minimum majordiameter of the GO thread plug gage or internal func-tional indicating gage shall be equal to the minimumpitch diameter of the internal thread plus an amountequal to 0.64951905P. The maximum major diameter ofthe NOT GO thread plug gage shall be equal to themaximum pitch diameter of the internal thread plusan amount equal to 0.43301270P. The maximum minordiameter of the GO thread ring gage or external func-tional diameter indicating gage shall be equal to themaximum pitch diameter of the external thread minusan amount equal to 0.43301300P. The minimum minordiameter of the NOT GO thread ring gage shall be equalto the minimum pitch diameter of the external threadminus an amount equal to 0.21650635P.



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ASME B1.20.1-2013

Table 6 Dimensions of External and Internal Straight Pipe Threads for Fixtures, NPSM(Free-Fitting Mechanical Joints)

External Thread Internal ThreadAxis

90 deg

Crest

Root

Fcs = 0.12500P

fcs = 0.10825P

hs = 0.64952P

hn = 0.54126PH = 0.866025P

60 deg

30 deg

30 deg

Crest

Root

Frs = 0.12500P

Frn = 0.12500P

frn = 0.10825P

fcn = 0.21651P

frs = 0.10825PFcn = 0.2500P

P

External Thread, Class 2A Internal Thread, Class 2BO.D. of

Major Diameter Pitch Diameter Minor Diameter Pitch DiameterNominal Pipe, Threads/Pipe Size D Inch Allowance Max. Min. Max. Min. Min. Max. Min.I Max.

1 2 3 4 5 6 7 8 9 10 11 12

1⁄8 0.405 27 0.0011 0.397 0.390 0.3725 0.3689 0.358 0.364 0.3736 0.37831⁄4 0.540 18 0.0013 0.526 0.517 0.4903 0.4859 0.468 0.481 0.4916 0.49743⁄8 0.675 18 0.0014 0.662 0.653 0.6256 0.6211 0.603 0.612 0.6270 0.63291⁄2 0.840 14 0.0015 0.823 0.813 0.7769 0.7718 0.747 0.759 0.7784 0.78513⁄4 1.050 14 0.0016 1.034 1.024 0.9873 0.9820 0.958 0.970 0.9889 0.9958

1 1.315 11.5 0.0017 1.293 1.281 1.2369 1.2311 1.201 1.211 1.2386 1.246211⁄4 1.660 11.5 0.0018 1.638 1.626 1.5816 1.5756 1.546 1.555 1.5834 1.591211⁄2 1.900 11.5 0.0018 1.877 1.865 1.8205 1.8144 1.785 1.794 1.8223 1.83022 2.375 11.5 0.0019 2.351 2.339 2.2944 2.2882 2.259 2.268 2.2963 2.304421⁄2 2.875 8 0.0022 2.841 2.826 2.7600 2.7526 2.708 2.727 2.7622 2.7720

3 3.500 8 0.0023 3.467 3.452 3.3862 3.3786 3.334 3.353 3.3885 3.398431⁄2 4.000 8 0.0023 3.968 3.953 3.8865 3.8788 3.835 3.848 3.8888 3.89884 4.500 8 0.0023 4.466 4.451 4.3848 4.3771 4.333 4.346 4.3871 4.39715 5.563 8 0.0024 5.528 5.513 5.4469 5.4390 5.395 5.408 5.4493 5.45986 6.625 8 0.0024 6.585 6.570 6.5036 6.4955 6.452 6.464 6.5060 6.5165

GENERAL NOTES:(a) NPSM threads have a form similar to that of UN threads and tolerances similar to 2A/2B. The internal thread has a minimum pitch

diameter equal to E1 of NPT threads.(b) The minor diameters of external threads and major diameters of internal threads are those as produced by commercial straight pipe

dies and commercial ground straight pipe taps. The major diameter of the external thread has been calculated on the basis of a trunca-tion of 0.10825P, and the minor diameter of the internal thread has been calculated on the basis of a truncation of 0.21651P, to pro-vide no interference at crest and root when product is gaged.

NOTE:(1) Column 11 is the same as the pitch diameter at the large end of internal thread, E1, Basic (see Table 2, column 8).

17



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ASME B1.20.1-2013

Table 7 Dimensions, External and Internal Straight Pipe Thread for Locknut Connections, NPSL(Loose-Fitting Mechanical Joints)

Locknut

Locknut

Tank floor or wall

Standard fitting with taper thread

Taper pipe thread

Straight locknut thread

External Threads Internal Threads

Nominal O.D. of MaximumI Minimum1

Pitch Diameter Pitch DiameterPipe Pipe, Threads/ Major MinorSize D Inch Diameter Max. Min. Diameter Min. Max.

1 2 3 4 5 6 7 8 9

1⁄8 0.405 27 0.409 0.3840 0.3805 0.362 0.3863 0.38981⁄4 0.540 18 0.541 0.5038 0.4986 0.470 0.5073 0.51253⁄8 0.675 18 0.678 0.6409 0.6357 0.607 0.6444 0.64961⁄2 0.840 14 0.844 0.7963 0.7896 0.753 0.8008 0.80753⁄4 1.050 14 1.054 1.0067 1.0000 0.964 1.0112 1.0179

1 1.315 11.5 1.318 1.2604 1.2523 1.208 1.2658 1.273911⁄4 1.660 11.5 1.663 1.6051 1.5970 1.553 1.6106 1.618711⁄2 1.900 11.5 1.902 1.8441 1.8360 1.792 1.8495 1.8576

2 2.375 11.5 2.376 2.3180 2.3099 2.265 2.3234 2.331521⁄2 2.875 8 2.877 2.7934 2.7817 2.718 2.8012 2.8129

3 3.500 8 3.503 3.4198 3.4081 3.344 3.4276 3.439331⁄2 4.000 8 4.003 3.9201 3.9084 3.845 3.9279 3.9396

4 4.500 8 4.502 4.4184 4.4067 4.343 4.4262 4.43795 5.563 8 5.564 5.4805 5.4688 5.405 5.4884 5.50016 6.625 8 6.620 6.5372 6.5255 6.462 6.5450 6.5567

8 8.625 8 8.615 8.5313 8.5196 8.456 8.5391 8.550810 10.750 8 10.735 10.6522 10.6405 10.577 10.6600 10.671712 12.750 8 12.732 12.6491 12.6374 12.574 12.6569 12.6686

NOTE:(1) As the American National Standard Straight Pipe Thread form of thread is produced by a single tool, the major and minor diameters of

the internal thread and the minor diameter of the external thread are presumed to vary with the pitch diameter. The major diameter ofthe external thread is usually determined by the diameter of the pipe. These theoretical diameters result from adding the depth of thetruncated thread (0.666025P) to the maximum pitch diameters in column 5, and it should be understood that commercial pipe will notalways have these maximum major diameters. The locknut thread is established on the basis of retaining the greatest possible amountof metal thickness between the bottom of the thread and the inside of the pipe. In order that a locknut may fit loosely on the exter-nally threaded part, an allowance equal to the increase in pitch diameter per turn is provided, with a tolerance of 1.5 turns for bothexternal and internal threads.

18



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ASME B1.20.1-2013

7 GAGES AND GAGE TOLERANCES FOR AMERICANNATIONAL STANDARD TAPER PIPE THREADS,NPT

7.1 Gage Design

Gages should be made of hardened steel and conformto the designs recommended in ASME B47.1 (see Figs. 7and 8).

7.1.1 Gages for External Threads. The L1 ring gageand indicating gage elements have a length equal todimension L1.

7.1.2 Gages for Internal Threads. The L1 plug andindicating gage elements have a length equal to dimen-sion L2. The L1 plug gage has a gaging notch located adistance L1 from the small end. In locating the basicgaging notch, the plane of the notch should intersectthe crest of the gage thread. The notched area of thelarge end of the plug gage shall remain sharp; however,it should not have burrs extending outside the threadform.

7.1.3 Partial End Threads. Partial end threads shallbe removed on both ends of the ring gage and both endsof the plug gage. This shall be done by chamfering tothe minor diameter of plugs and major diameter of ringsor “convolution” to full-form profile. This avoids possi-ble seating error from bent or malformed feathered edgeand protects the thread from chipping.

7.1.4 Marking of Gages. Each gage shall be markedso as to indicate clearly the nominal size of pipe, threadsper inch, and the proper thread series designation asgiven in the respective section of this Standard. Forrings, the marking shall be on the face of the large end.

7.2 Master Gages

Master gages are used to inspect working gages atthe times of manufacture and calibration. They are alsoused in setting indicating gages. Additionally, masterrings inspect master plugs, and master plugs inspectmaster rings. The L1 plug and ring master gages aremade to the basic dimensions specified in Table 8. Thethread roots of these gages shall clear a 0.0381P flator may be undercut beyond a sharp V. The crests aretruncated by 0.100P.

7.2.1 Master Gage Tolerances. Master gages shouldbe made to the basic dimensions as accurately as possi-ble, but in no case shall the cumulative variation exceedone-half of the total cumulative tolerance specified incolumns 13 and 14 of Table 9. A master ring and masterplug are mated, the large end of the ring seating flushat the plug notch within ±0.002 in. for sizes 1⁄16 through2, within ±0.003 in. for sizes 21⁄2 through 12, and within±0.005 in. for sizes 14 and larger. A supplementary checkby optical or other means should be made of flank angle

19

and form. Each master gage should be accompanied bya record of the measurements of all elements of thethread and the standoff of master plug or master ring(large end of ring gage to basic notch of plug gage).

CAUTION: It should be understood that only a specificallymatched set of masters (L1 plug and L1 ring) can be expected tomate with each other within the tolerance specified above andin General Note (a) of Table 9. There are many characteristics orvariations in gage elements that may combine to cause a signifi-cant standoff difference between master gages that are not specif-ically matched.

7.3 Working Gages

Working gages are used to inspect product threads.They are made to the basic dimensions given in Table 8.The roots of all gage threads shall clear 0.0381P width.A sharp V or undercut clearance is acceptable. The crestsare to be truncated an amount equal to 0.140P for 27threads per inch (tpi), 0.109P for 18 tpi, and 0.100P for14-tpi, 111⁄2-tpi, and 8-tpi threads (see Fig. 8). It is to benoted that these gages are truncated at the crest so thatthey bear only on the flanks of the thread. Thus, theydo not check the product crest or root truncations. Whenit is deemed necessary to determine whether or not suchtruncations are within the limits specified, or particu-larly that the maximum truncations are not exceeded,optical projection is one common method.

7.3.1 Working Gage Tolerances. Working gagesshould be made to the basic dimensions specified inTable 8 and within tolerances specified in Table 9. Themaximum wear on a working plug gage shall not bemore than the equivalent of 1⁄4 turn small from basic,when checked with a master gage. The maximum wearon a working ring gage shall not be more than 1⁄4 turnlarge from basic, when checked with a master gage. Asupplementary check by optical or other means shouldbe made of flank angle and form.

7.4 Relation of Lead and Angle Variations to PitchDiameter Tolerances of Gages

When it is necessary to compute from measurementsthe decimal part of a turn that a gage varies from thebasic dimensions, Tables 10 and 11 should be used.Table 10 gives the correction in diameter for angle varia-tions, and Table 11 gives the correction in diameter forlead variations. These corrections are always added tothe pitch diameter in the case of external threads andsubtracted in the case of internal threads, regardless ofwhether the lead or angle variations are either plus orminus. The diameter equivalent for lead and angle varia-tions plus the pitch diameter variation multiplied by 16gives the longitudinal variation from basic at the gagingnotch. This longitudinal variation divided by the pitchequals the decimal part of a turn that the gage variesfrom basic at the gaging notch.



--``,,,,`,`,,`,`````,`,,`,`,`-`-`,,`,,`,`,,`---

ASME B1.20.1-2013

Fig. 7 NPT Standard Taper Pipe Thread Plug and Ring Gages

Plug gage

Notch

L1

L1

E0

E1

Ring gage

L2

Taper of thread 1 in 16 measured on diameter

20



--``,,,,`,`,,`,`````,`,,`,`,`-`-`,,`,,`,`,,`---

ASME B1.20.1-2013

Fig. 8 Suggested Form of Gage Thread

Crests truncated Crests truncated

Roots sharp or undercut (form optional)

Ring gage

Plug gage

0.116P

GENERAL NOTE: Roots must clear 0.0381P width.

21



--``,,,,`,`,,`,`````,`,,`,`,`-`-`,,`,,`,`,,`---

ASME B1.20.1-2013

Tabl

e8

Bas

icD

imen

sion

sof

Thre

aded

Gag

esfo

rAm

eric

anN

atio

nal

Stan

dard

Tape

rPi

peTh

read

s,N

PT

Min

orD

iam

eter

sof

Rin

gM

ajor

Dia

met

ers

ofPl

ugan

dIn

tern

alPi

tch

Dia

met

ers

ofPl

ug,

Rin

g,an

dan

dEx

tern

alIn

dica

ting

Indi

cati

ngG

ages

Indi

cati

ngG

ages

[Not

e(1

)]G

ages

Thic

knes

sof

Incr

ease

inN

omin

alA

tS

mal

lA

tG

agin

gA

tLa

rge

At

Sm

all

At

Gag

ing

At

Larg

eA

tS

mal

lA

tG

agin

gL 1

Rin

gor

Dia

./Th

read

Pipe

O.D

.of

Thre

ads/

End,

E 0N

otch

,E 1

End,

E 2En

d,E 0

Not

ch,

E 1En

d,E 2

End,

E 0N

otch

,E 1

Gag

eS

ize

Pipe

,D

Inch

,n

Pitc

h,P

Plan

ePl

ane

Plan

ePl

ane

Plan

ePl

ane

Plan

ePl

ane

0.06

25/n

Elem

ents

12

34

56

78

910

1112

1314

1 ⁄ 16

0.31

2527

.00.

0370

3704

0.29

289

0.30

289

0.30

920

0.27

118

0.28

118

0.28

750

0.24

948

0.25

948

0.00

231

0.16

001 ⁄ 8

0.40

5027

.00.

0370

3704

0.38

521

0.39

531

0.40

171

0.36

351

0.37

360

0.38

000

0.34

180

0.35

190

0.00

231

0.16

151 ⁄ 4

0.54

0018

.00.

0555

5556

0.51

339

0.52

763

0.53

850

0.47

739

0.49

163

0.50

250

0.44

139

0.45

563

0.00

347

0.22

783 ⁄ 8

0.67

5018

.00.

0555

5556

0.64

802

0.66

302

0.67

350

0.61

201

0.62

701

0.63

750

0.57

601

0.59

101

0.00

347

0.24

001 ⁄ 2

0.84

0014

.00.

0714

2857

0.80

600

0.82

600

0.83

936

0.75

843

0.77

843

0.79

178

0.71

086

0.73

086

0.00

446

0.32

00

3 ⁄ 41.

0500

14.0

0.07

1428

571.

0152

51.

0364

41.

0493

60.

9676

80.

9888

71.

0017

80.

9201

10.

9412

90.

0044

60.

3390

11.

3150

11.5

0.08

6956

521.

2715

51.

2965

51.

3142

21.

2136

31.

2386

31.

2563

11.

1557

21.

1807

20.

0054

30.

4000

11 ⁄ 41.

6600

11.5

0.08

6956

521.

6150

51.

6413

01.

6592

21.

5571

31.

5833

81.

6013

11.

4992

21.

5254

70.

0054

30.

4200

11 ⁄ 21.

9000

11.5

0.08

6956

521.

8540

01.

8802

51.

8992

21.

7960

91.

8223

41.

8413

11.

7381

71.

7644

20.

0054

30.

4200

22.

3750

11.5

0.08

6956

522.

3269

42.

3541

92.

3742

22.

2690

22.

2962

72.

3163

02.

2111

12.

2383

60.

0054

30.

4360

21 ⁄ 22.

8750

8.0

0.12

5000

002.

8027

82.

8454

12.

8738

82.

7195

32.

7621

62.

7906

32.

6362

82.

6789

00.

0078

10.

6820

33.

5000

8.0

0.12

5000

003.

4238

83.

4717

53.

4988

83.

3406

33.

3885

03.

4156

33.

2573

73.

3052

50.

0078

10.

7660

31 ⁄ 24.

0000

8.0

0.12

5000

003.

9207

53.

9720

73.

9988

83.

8375

03.

8888

13.

9156

33.

7542

53.

8055

60.

0078

10.

8210

44.

5000

8.0

0.12

5000

004.

4176

34.

4703

84.

4988

84.

3343

84.

3871

34.

4156

34.

2511

24.

3038

70.

0078

10.

8440

55.

5630

8.0

0.12

5000

005.

4739

85.

5325

55.

5618

85.

3907

35.

4492

95.

4786

35.

3074

85.

3660

40.

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10.

9370

66.

6250

8.0

0.12

5000

006.

5293

56.

5892

26.

6238

86.

4460

96.

5059

76.

5406

36.

3628

46.

4227

20.

0078

10.

9580

88.

6250

8.0

0.12

5000

008.

5168

58.

5832

88.

6238

88.

4335

98.

5000

38.

5406

38.

3503

48.

4167

80.

0078

11.

0630

1010

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08.

00.

1250

0000

10.6

2857

10.7

0419

10.7

4888

10.5

4531

10.6

2094

10.6

6563

10.4

6206

10.5

3768

0.00

781

1.21

0012

12.7

500

8.0

0.12

5000

0012

.616

0712

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0712

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8112

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8112

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6312

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560.

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11.

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00.

1250

0000

13.8

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13.9

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13.9

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13.7

7500

13.8

7263

13.9

1563

13.6

9175

13.7

8937

0.00

781

1.56

20

1616

.000

08.

00.

1250

0000

15.8

4575

15.9

5900

15.9

9888

15.7

6250

15.8

7575

15.9

1563

15.6

7925

15.7

9250

0.00

781

1.81

2018

18.0

000

8.0

0.12

5000

0017

.833

2517

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2517

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8817

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6317

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750.

0078

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2020

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08.

00.

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0000

19.8

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19.9

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19.9

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19.7

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19.8

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19.9

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19.6

5425

19.7

8706

0.00

781

2.12

5024

24.0

000

8.0

0.12

5000

0023

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8823

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9423

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0078

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GEN

ERA

LN

OTE

:G

age

blan

kssh

allc

onfo

rmto

dim

ensi

ons

give

nin

ASM

EB

47.1

.Th

em

ajor

diam

eter

sof

inte

rnal

thre

adga

ges

and

the

min

ordi

amet

ers

ofex

tern

alth

read

gage

sar

eba

sed

upon

the

trun

cati

ons

spec

ified

inpa

ra.

7.2.

NO

TE:

(1)

The

pitc

hdi

amet

erat

the

larg

een

d,E 2

,do

esno

tap

ply

tori

ngga

ges.

22



--``,,,,`,`,,`,`````,`,,`,`,`-`-`,,`,,`,`,,`---

ASME B1.20.1-2013

Tabl

e9

Wor

king

Gag

eTo

lera

nces

for

Amer

ican

Nat

iona

lS

tand

ard

Tape

rPi

peTh

read

,N

PT

Sta

ndof

fB

etw

een

Plug

and

Ring

Tole

ranc

eon

Tole

ranc

eTo

lera

nce

Gag

esat

Gag

ing

Hal

fA

ngle

,4To

lera

nce

onon

Maj

oron

Min

orTo

tal

Cum

ulat

ive

Tole

ranc

eN

otch

for

Tole

ranc

eon

Min

utes

Tape

r,3,

5D

ia.

Dia

.To

lera

nces

onN

omin

alO

.D.

ofon

Pitc

hD

imen

sion

sat

Lead

2,3

Pitc

hD

ia.

Pipe

Pipe

,D

ia.,1

Plug

s,R

ings

,Pl

ugs,

Ring

s,Pl

ugs,

Ring

s,O

ppos

ite

Extr

eme

Siz

eD

Thre

ads/

Inch

±Pl

ugs

Rin

gs±

±+

−−

+Pl

ugs

Ring

sTo

lera

nce

Lim

its6

12

34

56

78

910

1112

1314

15

1 ⁄ 16

0.31

2527

0.00

020.

0002

0.00

0315

200.

0003

0.00

060.

0004

0.00

040.

0008

00.

0011

80.

032

1 ⁄ 80.

405

270.

0002

0.00

020.

0003

1520

0.00

030.

0006

0.00

040.

0004

0.00

080

0.00

118

0.03

21 ⁄ 4

0.54

018

0.00

020.

0002

0.00

0315

200.

0004

0.00

070.

0006

0.00

060.

0009

20.

0013

40.

036

3 ⁄ 80.

675

180.

0002

0.00

020.

0003

1520

0.00

040.

0007

0.00

060.

0006

0.00

092

0.00

134

0.03

61 ⁄ 2

0.84

014

0.00

030.

0002

0.00

0310

150.

0006

0.00

090.

0010

0.00

100.

0009

70.

0014

20.

038

3 ⁄ 41.

050

140.

0003

0.00

020.

0003

1015

0.00

060.

0009

0.00

100.

0010

0.00

097

0.00

142

0.03

81

1.31

511

.50.

0003

0.00

030.

0004

1015

0.00

080.

0012

0.00

100.

0010

0.00

121

0.00

170

0.04

711 ⁄ 4

1.66

011

.50.

0003

0.00

030.

0004

1015

0.00

080.

0012

0.00

100.

0010

0.00

121

0.00

170

0.04

711 ⁄ 2

1.90

011

.50.

0003

0.00

030.

0004

1015

0.00

080.

0012

0.00

100.

0010

0.00

121

0.00

170

0.04

72

2.37

511

.50.

0003

0.00

030.

0004

1015

0.00

080.

0012

0.00

100.

0010

0.00

121

0.00

170

0.04

7

21 ⁄ 22.

875

80.

0005

0.00

040.

0005

710

0.00

100.

0014

0.00

160.

0016

0.00

158

0.00

211

0.05

93

3.50

08

0.00

050.

0004

0.00

057

100.

0010

0.00

140.

0016

0.00

160.

0015

80.

0021

10.

059

31 ⁄ 24.

000

80.

0005

0.00

040.

0005

710

0.00

100.

0014

0.00

160.

0016

0.00

158

0.00

211

0.05

94

4.50

08

0.00

050.

0004

0.00

057

100.

0010

0.00

140.

0016

0.00

160.

0015

80.

0021

10.

059

55.

563

80.

0005

0.00

040.

0005

710

0.00

100.

0014

0.00

160.

0016

0.00

158

0.00

211

0.05

9

66.

625

80.

0005

0.00

040.

0005

710

0.00

100.

0014

0.00

160.

0016

0.00

158

0.00

211

0.05

98

8.62

58

0.00

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0004

0.00

057

100.

0010

0.00

140.

0020

0.00

200.

0015

80.

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10.

059

1010

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80.

0005

0.00

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0005

710

0.00

100.

0014

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200.

0020

0.00

158

0.00

211

0.05

912

12.7

508

0.00

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0004

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100.

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0.00

140.

0020

0.00

200.

0015

80.

0021

10.

059

140.

D.

14.0

008

0.00

080.

0005

0.00

067

100.

0010

0.00

140.

0030

0.00

300.

0020

60.

0027

10.

076

160.

D.

16.0

008

0.00

080.

0005

0.00

067

100.

0010

0.00

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0030

0.00

300.

0020

60.

0027

10.

076

180.

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18.0

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0.00

067

100.

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0030

0.00

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0027

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076

200.

D.

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0005

0.00

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100.

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0030

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0027

10.

076

240.

D.

24.0

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0.00

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0005

0.00

067

100.

0010

0.00

140.

0030

0.00

300.

0020

60.

0027

10.

076

23



--``,,,,`,`,,`,`````,`,,`,`,`-`-`,,`,,`,`,,`---

ASME B1.20.1-2013

Tabl

e9

Wor

king

Gag

eTo

lera

nces

for

Amer

ican

Nat

iona

lS

tand

ard

Tape

rPi

peTh

read

,N

PT(C

ont’

d)

GEN

ERA

LN

OTE

S:

(a)

The

larg

een

dof

the

mas

ter

ring

gage

shal

lbe

flush

wit

hth

ega

ging

notc

hof

its

mas

ter

plug

whe

nas

sem

bled

hand

tigh

tw

ithi

n±0

.002

for

size

s1 ⁄ 1

6to

2,in

clus

ive,

wit

hin

±0.0

03fo

rsi

zes

21 ⁄ 2to

12,

incl

usiv

e,an

dw

ithi

n±0

.005

for

size

s14

and

larg

er.

(b)

The

tole

ranc

esfo

rth

ele

ngth

L 1fr

omsm

all

end

toga

ging

notc

hof

the

plug

gage

d(F

ig.

4)sh

all

be+0

.000

and

−0.

001

for

size

s1 ⁄ 1

6to

2,in

clus

ive,

and

+0.0

00an

d−

0.00

2fo

rsi

zes

21 ⁄ 2an

dla

rger

.(c

)Th

eto

lera

nces

for

the

over

all

thre

adle

ngth

L 2of

the

plug

gage

(Fig

.4)

shal

lbe

+0.0

50an

d−

0.00

0fo

ral

lsi

zes.

(d)

Tole

ranc

esfo

rth

eth

ickn

ess

L 1of

the

ring

gage

(Fig

.4)

shal

lbe

−0.

000

and

+0.0

01fo

rsi

zes

1 ⁄ 16

to2,

incl

usiv

e,an

d−

0.00

0an

d+0

.002

for

size

s2

1 ⁄ 2an

dla

rger

.

NO

TES

:(1

)To

bem

easu

red

atth

ega

ging

notc

hof

plug

gage

.(2

)A

llow

able

vari

atio

nin

lead

betw

een

any

two

thre

ads

inL 1

leng

thof

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(Fig

.4)

.(3

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atio

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24



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ASME B1.20.1-2013

Table 10 Diameter Equivalent of Variation in Half Included Angle of Thread for Tools and Gages

Variation1 in Half Angle(in Minutes) 8 Threads/Inch 11.5 Threads/Inch 14 Threads/Inch 18 Threads/Inch 27 Threads/Inch

1 2 3 4 5 6

1 0.0000559 0.0000389 0.0000320 0.0000249 0.00001662 0.0001119 0.0000778 0.0000639 0.0000497 0.00003313 0.0001678 0.0001167 0.0000959 0.0000746 0.00004974 0.0002237 0.0001556 0.0001278 0.0000994 0.00006635 0.0002796 0.0001945 0.0001598 0.0001243 0.0000829

6 0.0003356 0.0002334 0.0001917 0.0001491 0.00009947 0.0003915 0.0002723 0.0002237 0.0001740 0.00011608 0.0004474 0.0003112 0.0002557 0.0001989 0.00013269 0.0005033 0.0003502 0.0002876 0.0002237 0.0001491

10 0.0005593 0.0003891 0.0003196 0.0002486 0.0001657

11 0.0006152 0.0004280 0.0003515 0.0002734 0.000182312 0.0006711 0.0004669 0.0003835 0.0002983 0.000198913 0.0007271 0.0005058 0.0004155 0.0003231 0.000215414 0.0007830 0.0005447 0.0004474 0.0003480 0.000232015 0.0008389 0.0005836 0.0004794 0.0003729 0.0002486

16 0.0008948 0.0006225 0.0005113 0.0003977 0.000265117 0.0009508 0.0006614 0.0005433 0.0004226 0.000281718 0.0010067 0.0007003 0.0005753 0.0004474 0.000298319 0.0010626 0.0007392 0.0006072 0.0004723 0.000314920 0.0011186 0.0007781 0.0006392 0.0004971 0.0003314

21 0.0011745 0.0008170 0.0006711 0.0005220 0.000348022 0.0012304 0.0008559 0.0007031 0.0005469 0.000364623 0.0012863 0.0008949 0.0007351 0.0005717 0.000381124 0.0013423 0.0009338 0.0007670 0.0005966 0.000397725 0.0013982 0.0009727 0.0007990 0.0006214 0.0004143

26 0.0014541 0.0010116 0.0008309 0.0006463 0.000430927 0.0015101 0.0010505 0.0008629 0.0006711 0.000447428 0.0015660 0.0010894 0.0008949 0.0006960 0.000464029 0.0016219 0.0011283 0.0009268 0.0007209 0.000480630 0.0016779 0.0011672 0.0009588 0.0007457 0.0004971

45 0.0025169 0.0017509 0.0014382 0.0011186 0.000745750 0.0027966 0.0019454 0.0015980 0.0012429 0.0008286

GENERAL NOTES:(a) Values given in inches at 68°F.(b) In solving for the diameter equivalent of angle variations, the average variation in half included angle for the two sides of the thread,

regardless of their signs, should be taken.(c) Table is based upon an NPT gage with 0.100P root/crest truncations with equal half-angle variations. For other gages with equal

truncations, multiply by0.86600P − 2 (truncation)

0.66666667PNOTE:(1) Diameter equivalent p 1.53811978P tan ��, where �� p variation in half included angle of thread expressed in minutes.

25



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ASME B1.20.1-2013

Tabl

e11

Dia

met

erEq

uiva

lent

ofVa

riat

ion

inLe

adfo

rTo

ols

and

Gag

es

Vari

atio

n,�

P0.

0000

00.

0000

10.

0000

20.

0000

30.

0000

40.

0000

50.

0000

60.

0000

70.

0000

80.

0000

9

12

34

56

78

910

11

0.00

000

0.00

0000

00.

0000

173

0.00

0034

60.

0000

520

0.00

0069

30.

0000

866

0.00

0103

90.

0001

212

0.00

0138

60.

0001

559

0.00

010

0.00

0173

20.

0001

905

0.00

0207

80.

0002

252

0.00

0242

50.

0002

598

0.00

0277

10.

0002

944

0.00

0311

80.

0003

291

0.00

020

0.00

0346

40.

0003

637

0.00

0381

00.

0003

984

0.00

0415

70.

0004

330

0.00

0450

30.

0004

676

0.00

0485

00.

0005

023

0.00

030

0.00

0519

60.

0005

369

0.00

0554

20.

0005

716

0.00

0588

90.

0006

062

0.00

0623

50.

0006

408

0.00

0658

20.

0006

755

0.00

040

0.00

0692

80.

0007

101

0.00

0727

40.

0007

448

0.00

0762

10.

0007

794

0.00

0796

70.

0008

140

0.00

0831

40.

0008

487

0.00

050

0.00

0866

00.

0008

833

0.00

0900

60.

0009

180

0.00

0935

30.

0009

526

0.00

0969

90.

0009

872

0.00

1004

60.

0010

219

0.00

060

0.00

1039

20.

0010

565

0.00

1073

80.

0010

912

0.00

1108

50.

0011

258

0.00

1143

10.

0011

604

0.00

1177

80.

0011

951

0.00

070

0.00

1212

40.

0012

297

0.00

1247

00.

0012

644

0.00

1281

70.

0012

990

0.00

1316

30.

0013

336

0.00

1351

00.

0013

683

0.00

080

0.00

1385

60.

0014

029

0.00

1420

20.

0014

376

0.00

1454

90.

0014

722

0.00

1489

50.

0015

068

0.00

1524

20.

0015

415

0.00

090

0.00

1558

80.

0015

761

0.00

1593

40.

0016

108

0.00

1628

10.

0016

454

0.00

1662

70.

0016

800

0.00

1697

40.

0017

147

0.00

100

0.00

1732

00.

0017

493

0.00

1766

60.

0017

840

0.00

1801

30.

0018

186

0.00

1835

90.

0018

532

0.00

1870

60.

0018

879

0.00

110

0.00

1905

20.

0019

225

0.00

1939

80.

0019

572

0.00

1974

50.

0019

918

0.00

2009

10.

0020

264

0.00

2043

80.

0020

611

0.00

120

0.00

2078

40.

0020

957

0.00

2113

00.

0021

304

0.00

2147

70.

0021

650

0.00

2182

30.

0021

996

0.00

2217

00.

0022

343

0.00

130

0.00

2251

60.

0022

689

0.00

2286

20.

0023

036

0.00

2320

90.

0023

382

0.00

2355

50.

0023

728

0.00

2390

20.

0024

075

0.00

140

0.00

2424

80.

0024

421

0.00

2459

40.

0024

768

0.00

2494

10.

0025

114

0.00

2528

70.

0025

460

0.00

2563

40.

0025

807

0.00

150

0.00

2598

00.

0026

153

0.00

2632

60.

0026

500

0.00

2667

30.

0026

846

0.00

2701

90.

0027

192

0.00

2736

60.

0027

539

0.00

160

0.00

2771

20.

0027

885

0.00

2805

80.

0028

232

0.00

2840

50.

0028

578

0.00

2875

10.

0028

924

0.00

2909

80.

0029

271

0.00

170

0.00

2944

40.

0029

617

0.00

2979

00.

0029

964

0.00

3013

70.

0030

310

0.00

3048

30.

0030

656

0.00

3083

00.

0031

003

0.00

180

0.00

3117

60.

0031

349

0.00

3152

20.

0031

696

0.00

3186

90.

0032

042

0.00

3221

50.

0032

388

0.00

3256

20.

0032

735

0.00

190

0.00

3290

80.

0033

081

0.00

3325

40.

0033

428

0.00

3360

10.

0033

774

0.00

3394

70.

0034

120

0.00

3429

40.

0034

467

0.00

200

0.00

3464

00.

0034

813

0.00

3498

60.

0035

160

0.00

3533

30.

0035

506

0.00

3567

90.

0035

852

0.00

3602

60.

0036

199

GEN

ERA

LN

OTE

S:

(a)

Valu

esgi

ven

inin

ches

at68

°F.

(b)

Dia

met

ereq

uiva

lent

p1.

7320

5081

�P,

whe

re�P

pva

riat

ion

inle

adbe

twee

nan

ytw

oth

read

s.

26



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ASME B1.20.1-2013

NONMANDATORY APPENDIX ATHE TURNS OF ENGAGEMENT METHOD OF GAGING

PRODUCT THREADS

A-1 METHOD OF GAGING

The turns of engagement method of gaging taperthreads determines that there is an adequate numberof threads available at hand engagement. This methodeliminates the effects of product chamfers during gaging.However, differences between gages’ end threadremoval and gage crest truncations may give differentgaging results for the same product thread. This maynecessitate collaboration between supplier and user.

27

A-2 TOLERANCE

The theoretical basic turns of engagement are foundin column 7 of Table 2. For the turns of engagementmethod, the turns to remove the L1 gage from the productthread are counted and must be within the tolerance ofbasic number of turns, ±1 turn.



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ASME B1.20.1-2013

NONMANDATORY APPENDIX BTAP DRILL SIZES

Holes prepared for tapping can be either straight ortapered. Both are acceptable as long as the product stan-dards for thread dimensions are met after tapping. Theminor diameter of the product threads should be cut bythe tap minor diameter to ensure concentricity with thepitch diameter, as well as to generate the proper threadheight and truncations. The actual hole size prior totapping is dependent on many variables and shouldapproximate the diameter K0, column 24 of Table 2 (BasicMinor Diameter at Small End of Pipe). Hole sizes mayvary from K0 so the tap can cut an acceptable pipe threadwith the required thread height.

28



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ASME B1.20.1-2013

NONMANDATORY APPENDIX CTHREAD TYPES AND CORRESPONDING GAGES AND GAGING

See Table C-1.

Table C-1 Thread Types and Corresponding Gages and Gaging

Product Thread Tolerance Applied to Basic Size

Thread External InternalThread to Type ofBe Gaged Thread Internal External Gaged With Small Large Large Small

NPT Pressure Taper Taper L1 or indicating gages 1 Turn 1 Turn 1 Turn 1 Turn

NPSC Pressure Straight . . . L1 or indicating gages . . . . . . 11⁄2 Turns 11⁄2 Turns

NPTR Mechanical Taper Taper L1 or indicating gages 1 Turn 0 Turns 1 Turn 0 Turns[Note (1)] [Note (1)] [Note (2)] [Note (2)]

NPSM Mechanical Straight Straight GO/NOT GO or indicating gages . . . . . . . . . . . .

NPSL Mechanical Straight Straight GO/NOT GO or indicating gages . . . . . . . . . . . .

NOTES:(1) See Table 5, column 7 for the modified external thread basic position.(2) See Table 5, column 18 for the internal thread basic position below the face of the fitting.

29



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INTENTIONALLY LEFT BLANK

30



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--``,,,,`,`,,`,`````,`,,`,`,`-`-`,,`,,`,`,,`---

ASME B1.20.1-2013

N10313Copyright ASME International Provided by IHS under license with ASME Licensee=CTCI Corporation/5926309001, User=Wang, Hsien Yu


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