Machinery's Handbook, 31st Edition
American Pipe Threads 2091 Table 1b. Basic Dimensions, American National Standard Taper Pipe Threads, NPT ANSI/ASME B1.20.1-2013 (R2018)
Wrench Makeup Length for Internal Thread
Nominal Perfect External Threads a
Vanish Thread, (3.47 thds.), V
Overall Length External Thread, L 4
Height of Thread, h 0.02963 0.02963 0.04444 0.04444 0.05714 0.05714 0.06957 0.06957 0.06957 0.06957 0.100000 0.100000 0.100000 0.100000 0.100000 0.100000 0.100000
Basic Minor Dia. at Small End of Pipe, b K 0
Nominal Pipe Size
Length, c L 3
Dia., E 3
Length, L 5 0.1870 0.1898 0.2907 0.2967 0.3909 0.4029 0.5089 0.5329 0.5496 0.5826 0.8875 0.9500 1.0000 1.0500 1.1563 1.2625 1.4625 1.6750 1.8750 2.0000 2.2000 2.4000 2.6000 3.0000
Dia., E 5
0.1111 0.26424 0.1111 0.35656 0.1667 0.46697 0.1667 0.60160 0.2143 0.74504 0.2143 0.95429 0.2609 1.19733 0.2609 1.54083 0.2609 1.77978 0.2609 2.25272 0.2500 d 3.32500 0.2500 3.82188 0.2500 4.31875 0.2500 5.37511 0.2500 d 2.70391 0.2500 6.43047 0.2500 8.41797 0.2500 10.52969 0.2500 12.51719
0.1285 0.1285 0.1928 0.1928 0.2479 0.2479 0.3017 0.3017 0.3017 0.3017 0.4338 0.4338 0.4338 0.4338 0.4338 0.4338 0.4338 0.4338 0.4338 0.4338 0.4338 0.4338 0.4338 0.4338
0.3896 0.3924 0.5946 0.6006 0.7815 0.7935 0.9845 1.0085 1.0252 1.0582 1.5712 1.6337 1.6837 1.7337 1.8400 1.9462 2.1462 2.3587 2.5587 2.6837 2.8837 3.0837 3.2837 3.6837
0.28287 0.37537 0.49556 0.63056 0.78286 0.99286 1.24543 1.59043 1.83043 2.30543 2.77500 3.40000 3.90000 4.40000 5.46300 6.52500 8.52500 10.65000 12.65000 13.90000 15.90000 17.90000 19.90000 23.90000
0.2415 0.3338 0.4329 0.5675 0.7014 0.9106 1.1441 1.4876 1.7266 2.1995 2.6195 3.2406 3.7374 4.2343 5.2907 6.3460 8.3335
1 ∕ 16
1 ∕ 8 1 ∕ 4 3 ∕ 8 1 ∕ 2 3 ∕ 4
1
1 1 ∕ 4 1 1 ∕ 2
2
2 1 ∕ 2
3
3 1 ∕ 2
4 5 6 8
10 12
0.100000 10.4453 0.100000 12.4328 0.100000 13.6749 0.100000 15.6624 0.100000 17.6499 0.100000 19.6374 0.100000 23.6124
14 OD 0.2500 13.75938 16 OD 0.2500 15.74688 18 OD 0.2500 17.73438 20 OD 0.2500 19.72188 24 OD 0.2500 23.69688
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 crests of the thread intersects the cylinder forming the external surface of the pipe. L 5 = L 2 − 2 p . 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 MIL-P-7105 gives the wrench makeup as three threads for 3 in. and smaller. The E 3 dimensions are then as follows: Size 2 1 ⁄ 2 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 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 so expressed for the purpose of eliminating errors in computations. Engagement Between External and Internal Taper Threads.— The normal length of en - gagement between external and internal taper threads when screwed together handtight is shown as L 1 in Table 1a . This length is controlled by the construction and use of the pipe thread gages. It is recognized that in special applications, such as flanges for high- pressure work, longer thread engagement is used, in which case the pitch diameter E 1 (Table 1a) is maintained and the pitch diameter E 0 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
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