Standard Pipe Thread Fittings

American Standard Taper Pipe Threads (NPT)
Nominal size
(inside
diameter)
Actual OD Threads per inch Length of engagement
(tightened by hand)
Hand tight turns Wrench makeup turns Length of effective thread
1/16 0.3125 27 0.160     0.2611
18 0.405 27 0.180 0.260
¼ 0.540 18 0.200 4 3 0.401
38 0.675 18 0.240 3 0.408
½ 0.840 14 0.320 3 0.534
¾ 1.050 14 0.340 3 0.546
1 1.315 11.5 0.400 0.682
1.660 11.5 0.420 0.707
1.900 11.5 0.420 0.724
2 2.375 11.5 0.436 5 3 0.756
2.875 8 0.682 3 1.136
3 3.500 8 0.766 6 3 1.2000
4.000 8 0.821 1.2500
4 4.500 8 0.844 1.3000
5 5.563 8 0.937 1.4063

See illustrations of actual size fittings (when viewed at 100%).

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