Basic Dimension of National Standard (NPT) Pipe Threads : ASME B1.20.1
Pipe Threads ___
ASME B1.20.1 (NPT/API)| NPS | Number of Threads Perinch | Pitch of Thread | Depth of Thread | Truncation, max | Pitch diameter at plane of hand-tight engagement | Length from end of pipe to plane of hand- tight engagement | Length of useful thread | Length of vanish(or washout) thread | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| P | H | L | E | L1 | L2 | L2 | |||||||||
| in | mm | in | mm | in | mm | in | mm | in | Threads | in | Threads | in | Threads | ||
| 1/8” | 27 | 0.03704 | 0.941 | 0.02963 | 0.753 | 0.00360 | 0.091 | 0.37360 | 9.489 | 0.162 | 4.36 | 0.2639 | 7.12 | 0.1285 | 3.47 |
| 1/4” | 18 | 0.05556 | 1.411 | 0.04444 | 1.129 | 0.00490 | 0.124 | 0.49163 | 12.487 | 0.228 | 4.10 | 0.4018 | 7.23 | 0.1928 | 3.47 |
| 3/8” | 18 | 0.05556 | 1.411 | 0.04444 | 1.129 | 0.00490 | 0.124 | 0.62701 | 15.926 | 0.240 | 4.32 | 0.4078 | 7.34 | 0.1928 | 3.47 |
| 1/2” | 14 | 0.07143 | 1.814 | 0.05714 | 1.451 | 0.00560 | 0.142 | 0.77843 | 19.772 | 0.320 | 4.48 | 0.5337 | 7.47 | 0.2478 | 3.47 |
| 3/4” | 14 | 0.07143 | 1.814 | 0.05714 | 1.451 | 0.00560 | 0.142 | 0.98887 | 25.117 | 0.339 | 4.75 | 0.5457 | 7.64 | 0.2478 | 3.47 |
| 1” | 11.5 | 0.08696 | 2.209 | 0.06957 | 1.767 | 0.00630 | 0.160 | 1.23863 | 31.461 | 0.400 | 4.60 | 0.6828 | 7.85 | 0.3017 | 3.47 |
| 1-1/4” | 11.5 | 0.08696 | 2.209 | 0.06957 | 1.767 | 0.00630 | 0.160 | 1.58338 | 40.218 | 0.420 | 4.83 | 0.7068 | 8.13 | 0.3017 | 3.47 |
| 1-1/2” | 11.5 | 0.08696 | 2.209 | 0.06957 | 1.767 | 0.00630 | 0.160 | 1.82234 | 46.287 | 0.402 | 4.83 | 0.7235 | 8.32 | 0.3017 | 3.47 |
| 2” | 11.5 | 0.08696 | 2.209 | 0.06957 | 1.767 | 0.00630 | 0.160 | 2.29627 | 58.325 | 0.436 | 5.01 | 0.7565 | 8.70 | 0.3017 | 3.47 |
| 2-1/2” | 8 | 0.12500 | 3.175 | 0.10000 | 2.540 | 0.00780 | 0.198 | 2.76215 | 70.159 | 0.682 | 5.46 | 1.1375 | 9.10 | 0.4337 | 3.47 |
| 3” | 8 | 0.12500 | 3.175 | 0.10000 | 2.540 | 0.00780 | 0.198 | 3.38850 | 86.068 | 0.766 | 6.13 | 1.2000 | 9.60 | 0.4337 | 3.47 |
| 3-1/2” | 8 | 0.12500 | 3.175 | 0.10000 | 2.540 | 0.00780 | 0.198 | 3.88881 | 98.776 | 0.821 | 6.57 | 1.2500 | 10.00 | 0.4337 | 3.47 |
| 4” | 8 | 0.12500 | 3.175 | 0.10000 | 2.540 | 0.00780 | 0.198 | 4.38712 | 111.433 | 0.844 | 6.75 | 1.3000 | 10.40 | 0.4337 | 3.47 |
| 5” | 8 | 0.12500 | 3.175 | 0.10000 | 2.540 | 0.00780 | 0.198 | 5.44929 | 138.412 | 0.937 | 7.50 | 1.4063 | 11.25 | 0.4337 | 3.47 |
| 6” | 8 | 0.12500 | 3.175 | 0.10000 | 2.540 | 0.00780 | 0.198 | 6.50597 | 165.252 | 0.958 | 7.66 | 1.5125 | 12.10 | 0.4337 | 3.47 |
| 8” | 8 | 0.12500 | 3.175 | 0.10000 | 2.540 | 0.00780 | 0.198 | 8.50003 | 215.901 | 1.630 | 8.50 | 1.7125 | 13.70 | 0.4337 | 3.47 |
| 10” | 8 | 0.12500 | 3.175 | 0.10000 | 2.540 | 0.00780 | 0.198 | 10.62094 | 296.772 | 1.210 | 9.58 | 1.9250 | 15.40 | 0.4337 | 3.47 |
| 12” | 8 | 0.12500 | 3.175 | 0.10000 | 2.540 | 0.00780 | 0.198 | 12.61781 | 320.493 | 1.360 | 10.88 | 2.1250 | 17.00 | 0.4337 | 3.47 |
| 14” | 8 | 0.12500 | 3.175 | 0.10000 | 2.540 | 0.00780 | 0.198 | 13.87262 | 352.365 | 1.562 | 12.50 | 2.2500 | 18.00 | 0.4337 | 3.47 |
| 16” | 8 | 0.12500 | 3.175 | 0.10000 | 2.540 | 0.00780 | 0.198 | 15.87575 | 403.244 | 1.812 | 14.50 | 2.4500 | 19.60 | 0.4337 | 3.47 |
| 18” | 8 | 0.12500 | 3.175 | 0.10000 | 2.540 | 0.00780 | 0.198 | 17.87500 | 454.025 | 2.000 | 16.00 | 2.6500 | 21.20 | 0.4337 | 3.47 |
| 20” | 8 | 0.12500 | 3.175 | 0.10000 | 2.540 | 0.00780 | 0.198 | 19.87031 | 504.706 | 2.125 | 17.00 | 2.8500 | 22.80 | 0.4337 | 3.47 |
| 24” | 8 | 0.12500 | 3.175 | 0.10000 | 2.540 | 0.00780 | 0.198 | 23.68094 | 606.066 | 2.375 | 19.00 | 3.2500 | 26.00 | 0.4337 | 3.47 |
E = Pitch diameter at hand-tight plane. This is also the pitch diameter at the gauge plane.
L2 = Effective length of thread = Truncation from point of thread triangle to flat (not shown in diagram). Minimum = 0.033P for all pitches. See table for maximum.
NPT = symbol for the thread series and form (i.e., National (American) Standard Pipe, Taper)
L1 = Length of normal hand-tight engagement. This is also the L1 gauge length. (Longer thread engagement may be used in special applications, such as flanges for high pressure use. In such cases the pitch diameter, E, remains as specified and the diameter at the end of the pipe is proportionally smaller.)
Example designation:3/8 – 18 NPT where 3/8 = nominal pipe size 18 = number of threads per inch
Tolerances When using L1 gauges to check threads, the thread is within permissible tolerance if the ring gauge face, or plug gauge notch, is +/- 1 turn from being flush with the end of the thread.
Note: Basic dimensions are given to four or five decimal places to eliminate errors when calculating gauge dimensions, they do not imply a greater degree of precisions than is normally obtainable. Metric dimensions, where shown, are calculated from the inch values and rounded.