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%).