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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
1⁄8 0.405 27 0.180 4½ 2½ 0.260
¼ 0.540 18 0.200 4 3 0.401
3⁄8 0.675 18 0.240 4½ 3 0.408
½ 0.840 14 0.320 4½ 3 0.534
¾ 1.050 14 0.340 4½ 3 0.546
1 1.315 11.5 0.400 4½ 3¼ 0.682
1¼ 1.660 11.5 0.420 4½ 3¼ 0.707
1½ 1.900 11.5 0.420 4½ 3¼ 0.724
2 2.375 11.5 0.436 5 3 0.756
2½ 2.875 8 0.682 5½ 3 1.136
3 3.500 8 0.766 6 3 1.2000
3½ 4.000 8 0.821 6½ 3½ 1.2500
4 4.500 8 0.844 6¾ 3½ 1.3000
5 5.563 8 0.937 7½ 3¾ 1.4063

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