Machinery's Handbook, 31st Edition
2094 American Pipe Threads Table 5. American National Standard Straight Pipe Threads for Mechanical Joints, NPSM and NPSL ANSI/ASME B1.20.1-2013 (R2018) Nominal External Thread Internal Thread
Threads per Inch
Major Diameter
Pitch Diameter
Minor Diameter
Pitch Diameter
Pipe Size
Allow ance
Max. a
Min. a
Min. b
Min.
Max.
Min.
Max.
Max.
Free-fitting Mechanical Joints for Fixtures—NPSM
27 18 18 14 14
0.0011 0.0013 0.0014 0.0015 0.0016 0.0017 0.0018 0.0018 0.0019 0.0022 0.0023 0.0023 0.0023 0.0024 0.0024
0.397 0.390 0.3725 0.3689 0.358 0.364 0.3736 0.3783 0.526 0.517 0.4903 0.4859 0.468 0.481 0.4916 0.4974 0.662 0.653 0.6256 0.6211 0.603 0.612 0.6270 0.6329 0.823 0.813 0.7769 0.7718 0.747 0.759 0.7784 0.7851 1.034 1.024 0.9873 0.9820 0.958 0.970 0.9889 0.9958 1.293 1.281 1.2369 1.2311 1.201 1.211 1.2386 1.2462 1.638 1.626 1.5816 1.5756 1.546 1.555 1.5834 1.5912 1.877 1.865 1.8205 1.8144 1.785 1.794 1.8223 1.8302 2.351 2.339 2.2944 2.2882 2.259 2.268 2.2963 2.3044 2.841 2.826 2.7600 2.7526 2.708 2.727 2.7622 2.7720 3.467 3.452 3.3862 3.3786 3.334 3.353 3.3885 3.3984 3.968 3.953 3.8865 3.8788 3.835 3.848 3.8888 3.8988 4.466 4.451 4.3848 4.3771 4.333 4.346 4.3871 4.3971 5.528 5.513 5.4469 5.4390 5.395 5.408 5.4493 5.4598
1 ∕ 8 1 ∕ 4 3 ∕ 8 1 ∕ 2 3 ∕ 4
1
11 1 ∕ 2 11 1 ∕ 2 11 1 ∕ 2 11 1 ∕ 2
1 1 ∕ 4 1 1 ∕ 2
2
8 8 8 8 8 8
2 1 ∕ 2
3
3 1 ∕ 2
4 5 6
6.585 6.570 6.5036 6.4955 6.452 6.464 6.5060 6.5165 Loose-fitting Mechanical Joints for Locknut Connections—NPSL
27 18 18 14 14
… 0.409 … 0.3840 0.3805 0.362 … 0.541 … 0.5038 0.4986 0.470 … 0.678 … 0.6409 0.6357 0.607 … 0.844 … 0.7963 0.7896 0.753 … 1.054 … 1.0067 1.0000 0.964 … 1.318 … 1.2604 1.2523 1.208 … 1.663 … 1.6051 1.5970 1.553 … 1.902 … 1.8441 1.8360 1.792 … 2.376 … 2.3180 2.3099 2.265 … 2.877 … 2.7934 2.7817 2.718 … 3.503 … 3.4198 3.4081 3.344 … 4.003 … 3.9201 3.9084 3.845 … 4.502 … 4.4184 4.4067 4.343 … 5.564 … 5.4805 5.4688 5.405 … 6.620 … 6.5372 6.5255 6.462 … 8.615 … 8.5313 8.5196 8.456 … 10.735 … 10.6522 10.6405 10.577 … 12.732 … 12.6491 12.6374 12.574
… 0.3863 0.3898 … 0.5073 0.5125 … 0.6444 0.6496 … 0.8008 0.8075 … 1.0112 1.0179 … 1.2658 1.2739 … 1.6106 1.6187 … 1.8495 1.8576 … 2.3234 2.3315 … 2.8012 2.8129 … 3.4276 3.4393 … 3.9279 3.9396 … 4.4262 4.4379 … 5.4884 5.5001 … 6.5450 6.5567 … 8.5391 8.5508 … 10.6600 10.6717
1 ∕ 8 1 ∕ 4 3 ∕ 8 1 ∕ 2 3 ∕ 4
1
11 1 ∕ 2 11 1 ∕ 2 11 1 ∕ 2 11 1 ∕ 2
1 1 ∕ 4 1 1 ∕ 2
2
8 8 8 8 8 8 8 8
2 1 ∕ 2
3
3 1 ∕ 2
4 5 6 8
10 12
8 … 12.6569 12.6686 a As the ANSI Standard Straight Pipe Thread form of thread is maintained, the major and the minor diameters of the internal thread and the minor diameter of the external thread vary with the pitch diameter. The major diameter of the external thread is usually determined by the diameter of the pipe. These theoretical diameters result from adding the depth of the truncated thread (0.666025 × p ) to the maximum pitch diameters, and it should be understood that commercial pipe will not always have these maximum major diameters. b This is the same as the pitch diameter at end of internal thread, E 1 Basic . (See Table 1a.) All dimensions are given in inches. Notes for Free-fitting Fixture Threads: The minor diameters of external threads and major diame ters 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 truncation of 0.10825 p , and the minor diameter of the internal thread has been calculated on the basis of a trunca tion of 0.21651 p , to provide no interference at crest and root when product is gaged with gages made in accordance with the Standard. Notes for Loose-fitting Locknut Threads: The locknut thread is established on the basis of retaining the greatest possible amount of metal thickness between the bottom of the thread and the inside of the pipe. In order that a locknut may fit loosely on the externally threaded part, an allowance equal to the “increase in pitch diameter per turn” is provided, with a tolerance of 1 1 ∕ 2 turns for both external and internal threads.
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