PAGE NO 1867-1871

Machinery's Handbook 27th Edition1860

AMERICAN PIPE THREADS

PIPE AND HOSE THREADSThe types of threads used on pipe and pipe fittings may be classed according to theirintended use: 1) threads that when assembled with a sealer will produce a pressure-tightjoint; 2) threads that when assembled without a sealer will produce a pressure-tight joint;3) threads that provide free- and loose-fitting mechanical joints without pressure tightness; and 4) threads that produce rigid mechanical joints without pressure tightness.American National Standard Pipe ThreadsAmerican National Standard pipe threads described in the following paragraphs providetaper and straight pipe threads for use in various combinations and with certain modifications to meet these specific needs.Thread Designation and Notation.American National Standard Pipe Threads are designated by specifying in sequence the nominal size, number of threads per inch, and thesymbols for the thread series and form, as: 3818 NPT. The symbol designations are asfollows: NPTAmerican National Standard Taper Pipe Thread; NPTRAmericanNational Standard Taper Pipe Thread for Railing Joints; NPSCAmerican National Standard Straight Pipe Thread for Couplings; NPSMAmerican National Standard StraightPipe Thread for Free-fitting Mechanical Joints; NPSLAmerican National StandardStraight Pipe Thread for Loose-fitting Mechanical Joints with Locknuts; and NPSHAmerican National Standard Straight Pipe Thread for Hose Couplings.American National Standard Taper Pipe Threads.The basic dimensions of theANSI Standard taper pipe thread are given in Table 1a.Form of Thread: The angle between the sides of the thread is 60 degrees when measuredin an axial plane, and the line bisecting this angle is perpendicular to the axis. The depth ofthe truncated thread is based on factors entering into the manufacture of cutting tools andthe making of tight joints and is given by the formulas in Table 1a or the data in Table 2obtained from these formulas. Although the standard shows flat surfaces at the crest androot of the thread, some rounding may occur in commercial practice, and it is intended thatthe pipe threads of product shall be acceptable when crest and root of the tools or chaserslie within the limits shown in Table 2.Pitch Diameter Formulas: In the following formulas, which apply to the ANSI Standardtaper pipe thread, E0 = pitch diameter at end of pipe; E1 = pitch diameter at the large end ofthe internal thread and at the gaging notch; D = outside diameter of pipe; L1 = length ofhand-tight or normal engagement between external and internal threads; L2 = basic lengthof effective external taper thread; and p = pitch = 1 number of threads per inch.E 0 = D ( 0.05D + 1.1 )p

E 1 = E 0 + 0.0625L 1Thread Length: The formula for L2 determines the length of the effective thread andincludes approximately two usable threads that are slightly imperfect at the crest. The normal length of engagement, L1, between external and internal taper threads, when assembled by hand, is controlled by the use of the gages.L 2 = ( 0.80D + 6.8 )pTaper: The taper of the thread is 1 in 16, or 0.75 inch per foot, measured on the diameterand along the axis. The corresponding half-angle of taper or angle with the center line is 1degree, 47 minutes.

Copyright 2004, Industrial Press, Inc., New York, NY

;;;;;;;;;;Machinery's Handbook 27th EditionAMERICAN PIPE THREADS

1861

Table 1a. Basic Dimensions, American National Standard Taper Pipe Threads, NPTANSI/ASME B1.20.1-1983 (R2001)L4

L5

L3

Imperfect Threads dueto Chamfer on die

V

L2

2p

Taper of Thread 1 in 16Measured on Diameter

L1

E1 E5

E0

E3

E2

D

For all dimensions, see corresponding reference letter in table.Angle between sides of thread is 60 degrees. Taper of thread, on diameter, is 34 inch per foot. Angle of taper with center line is147.The basic maximum thread height, h, of the truncated thread is 0.8 pitch of thread. The crest and root are truncated a minimumof 0.033 pitch for all pitches. For maximum depth of truncation, see Table 2.

NominalPipeSize116

OutsideDia. ofPipe,D

ThreadsperInch,n

PitchofThread,p

PitchDiameter atBeginningof ExternalThread, E0

Handtight EngagementLength,aL1

Effective Thread, External

Dia.,bE1

Length,cL2

Inch

Dia.,E2Inch

0.3125

27

0.03704

0.27118

0.160

0.28118

0.2611

0.28750

18

0.405

27

0.03704

0.36351

0.1615

0.37360

0.2639

0.38000

14

0.540

18

0.05556

0.47739

0.2278

0.49163

0.4018

0.50250

38

0.675

18

0.05556

0.61201

0.240

0.62701

0.4078

0.63750

12

0.840

14

0.07143

0.75843

0.320

0.77843

0.5337

0.79179

34

1.050

14

0.07143

0.96768

0.339

0.98887

0.5457

1.00179

1

1.315

1112

0.08696

1.21363

0.400

1.23863

0.6828

1.25630

114

1.660

1112

0.08696

1.55713

0.420

1.58338

0.7068

1.60130

112

1.900

1112

0.08696

1.79609

0.420

1.82234

0.7235

1.84130

2

2.375

1112

0.08696

2.26902

0.436

2.29627

0.7565

2.31630

212

2.875

8

0.12500

2.71953

0.682

2.76216

1.1375

2.79062

3

3.500

8

0.12500

3.34062

0.766

3.38850

1.2000

3.41562

312

4.000

8

0.12500

3.83750

0.821

3.88881

1.2500

3.91562

4

4.500

8

0.12500

4.33438

0.844

4.38712

1.3000

4.41562

5

5.563

8

0.12500

5.39073

0.937

5.44929

1.4063

5.47862

6

6.625

8

0.12500

6.44609

0.958

6.50597

1.5125

6.54062

8

8.625

8

0.12500

8.43359

1.063

8.50003

1.7125

8.54062

10

10.750

8

0.12500

10.54531

1.210

10.62094

1.9250

10.66562

12

12.750

8

0.12500

12.53281

1.360

12.61781

2.1250

12.66562

14 OD

14.000

8

0.12500

13.77500

1.562

13.87262

2.2500

13.91562

16 OD

16.000

8

0.12500

15.76250

1.812

15.87575

2.4500

15.91562

18 OD

18.000

8

0.12500

17.75000

2.000

17.87500

2.6500

17.91562

20 OD

20.000

8

0.12500

19.73750

2.125

19.87031

2.8500

19.91562

24 OD

24.000

8

0.12500

23.71250

2.375

23.86094

3.2500

23.91562

a Also length of thin ring gage and length from gaging notch to small end of plug gage.b Also pitch diameter at gaging notch (handtight plane).c Also length of plug gage.




Table 1b. Basic Dimensions, American National Standard Taper Pipe Threads, NPTANSI/ASME B1.20.1-1983 (R2001)NominalPipeSize116

Wrench Makeup Lengthfor Internal ThreadLength,cL3

Dia.,E3

VanishThread,(3.47 thds.),V

Nominal PerfectExternal Threadsa

Overall LengthExternalThread,L4

Length,L5

Dia.,E5

HeightofThread,h

Basic MinorDia. at SmallEnd of Pipe,bK0

0.1111

0.26424

0.1285

0.3896

0.1870

0.28287

0.02963

0.2416

0.1111

0.35656

0.1285

0.3924

0.1898

0.37537

0.02963

0.3339

0.1667

0.46697

0.1928

0.5946

0.2907

0.49556

0.04444

0.4329

0.1667

0.60160

0.1928

0.6006

0.2967

0.63056

0.04444

0.5676

0.2143

0.74504

0.2478

0.7815

0.3909

0.78286

0.05714

0.7013

0.2143

0.95429

0.2478

0.7935

0.4029

0.99286

0.05714

0.9105

0.26090.2609

1.197331.54083

0.30170.3017

0.98451.0085

0.50890.5329

1.245431.59043

0.069570.06957

1.14411.4876

112

0.2609

1.77978

0.3017

1.0252

0.5496

1.83043

0.06957

1.7265

2

0.2609

2.252722.70391

0.30170.4337

1.05821.5712

0.58260.8875

2.305432.77500

0.069570.100000

2.19952.6195

18

14

38

12

34

1

114

2123

0.2500d0.2500d0.2500

3.32500

0.4337

1.6337

0.9500

3.40000

0.100000

3.2406

312

3.82188

0.4337

1.6837

1.0000

3.90000

0.100000

3.7375

4568101214 OD16 OD18 OD20 OD24 OD

0.25000.25000.25000.25000.25000.25000.25000.25000.25000.25000.2500

4.318755.375116.430478.4179710.5296912.5171913.7593815.7468817.7343819.7218823.69688

0.43370.43370.43370.43370.43370.43370.43370.43370.43370.43370.4337

1.73371.84001.94622.14622.35872.55872.68372.88373.08373.28373.6837

1.05001.15631.26251.46251.67501.87502.00002.20002.40002.60003.0000

4.400005.463006.525008.5250010.6500012.6500013.9000015.9000017.9000019.9000023.90000

0.1000000.1000000.1000000.1000000.1000000.1000000.1000000.1000000.1000000.1000000.100000

4.23445.29076.34618.333610.445312.432813.675015.662517.650019.637523.6125

a The length L

5 from the end of the pipe determines the plane beyond which the thread form is imperfect at the crest. The next two threads are perfect at the root. At this plane the cone formed by the crestsof the thread intersects the cylinder forming the external surface of the pipe. L5 = L2 2p.b Given as information for use in selecting tap drills.c Three threads for 2-inch size and smaller; two threads for larger sizes.d Military Specification MILP7105 gives the wrench makeup as three threads for 3 in. andsmaller. The E3 dimensions are then as follows: Size 212 in., 2.69609 and size 3 in., 3.31719.All dimensions given in inches.Increase in diameter per thread is equal to 0.0625/n.The basic dimensions of the ANSI Standard Taper Pipe Thread are given in inches to four or fivedecimal places. While this implies a greater degree of precision than is ordinarily attained, thesedimensions are the basis of gage dimensions and are so expressed for the purpose of eliminatingerrors in computations.

Engagement Between External and Internal Taper Threads.The normal length ofengagement between external and internal taper threads when screwed together handtightis shown as L1 in Table 1a. This length is controlled by the construction and use of the pipethread gages. It is recognized that in special applications, such as flanges for high-pressurework, longer thread engagement is used, in which case the pitch diameter E1 (Table 1a) ismaintained and the pitch diameter E0 at the end of the pipe is proportionately smaller.Tolerances on Thread Elements.The maximum allowable variation in the commercial product (manufacturing tolerance) is one turn large or small from the basic dimensions.The permissible variations in thread elements on steel products and all pipe made of steel,wrought iron, or brass, exclusive of butt-weld pipe, are given in Table 3. This table is a


Machinery's Handbook 27th EditionAMERICAN PIPE THREADS

1863

guide for establishing the limits of the thread elements of taps, dies, and thread chasers.These limits may be required on product threads.On pipe fittings and valves (not steel) for steam pressures 300 pounds and below, it isintended that plug and ring gage practice as set up in the Standard ANSI/ASME B1.20.1will provide for a satisfactory check of accumulated variations of taper, lead, and angle insuch product. Therefore, no tolerances on thread elements have been established for thisclass.For service conditions where a more exact check is required, procedures have beendeveloped by industry to supplement the regulation plug and ring method of gaging.Table 2. Limits on Crest and Root of American National Standard External andInternal Taper Pipe Threads, NPT ANSI/ASME B1.20.1-1983 (R2001)INTERNAL THREADMinimumTruncation

RootMinimumTruncation

HMax. h

MaximumTruncation

MinimumTruncation

MaximumTruncation

CrestCrestMaximumTruncationMaximumTruncationRootMinimumTruncation

EXTERNAL THREADThreadsperInch

Height of SharpV Thread, H

27181411128

Height of Pipe Thread,h

Truncation,f

Width of Flat, F,Equivalent toTruncation

Max.

Min.

Min.

Max.

Min.

Max.

0.032080.048110.061860.07531

0.029630.044440.057140.06957

0.024960.038330.050710.06261

0.00120.00180.00240.0029

0.00360.00490.00560.0063

0.00140.00210.00270.0033

0.00410.00570.00640.0073

0.10825

0.10000

0.09275

0.0041

0.0078

0.0048

0.0090

All dimensions are in inches and are given to four or five decimal places only to avoid errors incomputations, not to indicate required precision.

Table 3. Tolerances on Taper, Lead, and Angle of Pipe Threads of Steel Products andAll Pipe of Steel, Wrought Iron, or Brass ANSI/ASME B1.20.1-1983 (R2001)(Exclusive of Butt-Weld Pipe)Nominal Pipe Size

1,

1 , 116 81 , 34 81 , 32 4114, 112,

212 and

ThreadsperInch271814

2

larger

11128

Taper on Pitch Line (34 in./ft)Max.

Min.

+18

116

+18+18+18+18

116116116116

Lead in Lengthof EffectiveThreads0.003

60 Degree Angleof Threads,Degrees

0.003

2122

0.003a

2

0.003a

112

0.003a

112

a The tolerance on lead shall be 0.003 in. per inch on any size threaded to an effective thread lengthgreater than 1 in.For tolerances on height of thread, see Table 2.The limits specified in this table are intended to serve as a guide for establishing limits of the threadelements of taps, dies, and thread chasers. These limits may be required on product threads.




Table 4. Internal Threads in Pipe Couplings, NPSC for Pressuretight Joints withLubricant or Sealer ANSI/ASME B1.20.1-1983 (R2001)Nom.Pipe- Thds.perSizeInch1814381234

1

114

2718181414

11121112

Minora Dia.Min.0.3400.4420.5770.7150.9251.1611.506

Pitch DiameterbMin.Max.0.37010.37710.48640.62180.77170.98221.23051.5752

0.49680.63220.78510.99561.24681.5915

Nom.Pipe

Thds. perInch

1122

111211128888

2123

3124

Minora Dia.Min.1.7452.2192.6503.2773.7774.275

Pitch DiameterbMin.Max.1.81421.83052.28812.75043.37683.87714.3754

2.30442.77393.40023.90054.3988

a As the ANSI Standard Pipe Thread form is maintained, the major and minor diameters of the internal thread vary with the pitch diameter. All dimensions are given in inches.b The actual pitch diameter of the straight tapped hole will be slightly smaller than the value givenwhen gaged with a taper plug gage as called for in ANSI/ASME B1.20.1.

Railing Joint Taper Pipe Threads, NPTR.Railing joints require a rigid mechanicalthread joint with external and internal taper threads. The external thread is basically thesame as the ANSI Standard Taper Pipe Thread, except that sizes 12 through 2 inches areshortened by 3 threads and sizes 212 through 4 inches are shortened by 4 threads to permitthe use of the larger end of the pipe thread. A recess in the fitting covers the last scratch orimperfect threads on the pipe.Straight Pipe Threads in Pipe Couplings, NPSC.Threads in pipe couplings made inaccordance with the ANSI/ASME B1.20.1 specifications are straight (parallel) threads ofthe same thread form as the ANSI Standard Taper Pipe Thread. They are used to form pressuretight joints when assembled with an ANSI Standard external taper pipe thread andmade up with lubricant or sealant. These joints are recommended for comparatively lowpressures only.Straight Pipe Threads for Mechanical Joints, NPSM, NPSL, and NPSH.W h i l eexternal and internal taper pipe threads are recommended for pipe joints in practicallyevery service, there are mechanical joints where straight pipe threads are used to advantage. Three types covered by ANSI/ASME B1.20.1 are:Loose-fitting Mechanical Joints With Locknuts (External and Internal), NPSL: T h i sthread is designed to produce a pipe thread having the largest diameter that it is possible tocut on standard pipe. The dimensions of these threads are given in Table 5. It will be notedthat the maximum major diameter of the external thread is slightly greater than the nominaloutside diameter of the pipe. The normal manufacturer's variation in pipe diameter provides for this increase.Loose-fitting Mechanical Joints for Hose Couplings (External and Internal), NPSH:Hose coupling joints are ordinarily made with straight internal and external loose-fittingthreads. There are several standards of hose threads having various diameters and pitches.One of these is based on the ANSI Standard pipe thread and by the use of this thread series,it is possible to join small hose couplings in sizes 12 to 4 inches, inclusive, to ends of standard pipe having ANSI Standard External Pipe Threads, using a gasket to seal the joints.For the hose coupling thread dimensions see ANSI Standard Hose Coupling ScrewThreads starting on page 1872.Free-fitting Mechanical Joints for Fixtures (External and Internal), NPSM: S t a n d a r diron, steel, and brass pipe are often used for special applications where there are no internalpressures. Where straight thread joints are required for mechanical assemblies, straightpipe threads are often found more suitable or convenient. Dimensions of these threads aregiven in Table 5.


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