National Standard Taper Pipe Threads Size NPT Chart

Outside Diameter D	Nominal Pipe Size	Threads per Inch (Pitch)	Thread Pitch Length, P	Pitch Diameter at External Thread Start E0	Hand Tight Thread Engagement Length,L1	Diameter E1	Maximum Thread Engagement L2	Diameter E2
0.3125	1⁄16	27	0.03704	0.27118	0.160	0.28118	0.2611	0.28750
0.405	1⁄8	27	0.03704	0.36351	0.1615	0.37360	0.2639	0.38000
0.540	1⁄4	18	0.05556	0.47739	0.2278	0.49163	0.4018	0.50250
0.675	3⁄8	18	0.05556	0.61201	0.240	0.62701	0.4078	0.63750
0.840	1⁄2	14	0.07143	0.75843	0.320	0.77843	0.5337	0.79179
1.050	3⁄4	14	0.07143	0.96768	0.339	0.98887	0.5457	1.00179
1.315	1	11 1⁄2	0.08696	1.21363	0.400	1.23863	0.6828	1.25630
1.660	1 1⁄4	11 1⁄2	0.08696	1.55713	0.420	1.58338	0.7068	1.60130
1.900	1 1⁄2	11 1⁄2	0.08696	1.79609	0.420	1.82234	0.7235	1.84130
2.375	2	11 1⁄2	0.08696	2.26902	0.436	2.29627	0.7565	2.31630
2.875	2 1⁄2	8	0.12500	2.71953	0.682	2.76216	1.1375	2.79062
3.500	3	8	0.12500	3.34062	0.766	3.38850	1.2000	3.41562
4.000	3 1⁄2	8	0.12500	3.83750	0.821	3.88881	1.2500	3.91562
4.500	4	8	0.12500	4.33438	0.844	4.38712	1.3000	4.41562
5.563	5	8	0.12500	5.39073	0.937	5.44929	1.4063	5.47862
6.625	6	8	0.12500	6.44609	0.958	6.50597	1.5125	6.54062
8.625	8	8	0.12500	8.43359	1.063	8.50003	1.7125	8.54062
10.750	10	8	0.12500	10.54531	1.210	10.62094	1.9250	10.66562
12.750	12	8	0.12500	12.53281	1.360	12.61781	2.1250	12.66562
14.000	14	8	0.12500	13.77500	1.562	13.87262	2.2500	13.91562
16.000	16	8	0.12500	15.76250	1.812	15.87575	2.4500	15.91562
18.000	18	8	0.12500	17.75000	2.000	17.87500	2.6500	17.91562
20.000	20	8	0.12500	19.73750	2.125	19.87031	2.8500	19.91562
24.000	24	8	0.12500	23.71250	2.375	23.86094	3.2500	23.91562