National Standard Taper Pipe Threads Size NPT Chart

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National Standard Taper Pipe Threads Size NPT Chart - Includes both External and internal Pipe Thread Data. The taper rate for all NPT threads is 1⁄16 (3⁄4 inch per foot) measured by the change of diameter (of the pipe thread) over distance. The angle between the taper and the center axis of the pipe is 1° 47'′ 24"″ (1.7899°). Commonly-used sizes are 1/⁄8, 1/⁄4, 3/⁄8, 1⁄/2, 3⁄/4, 1, 1 1⁄/4, 1 1⁄/2, and 2 inch, appearing on pipes and fittings by most U.S. suppliers. Sizes smaller than 1/⁄8 inch are occasionally used for compressed air, while sizes larger than 2 inches are uncommon, due to the use of alternative methods of joining that are used with these larger sizes. NPT is defined by ANSI/ASME standard B1.20.1.

Nominal Pipe Size is loosely related to the inside diameter of Schedule 40 pipe. Because of the pipe wall thickness, the actual diameter of the threads is larger than the NPS, considerably so for small NPS. Other schedules of pipe have different wall thickness but the OD (outer diameter) and thread profile remain the same, so the inside diameter of the pipe is therefore different from the nominal diameter.

Notes:

Reference ANSI/ASME B1.20.1-1983 (R1992)
Angle between sides of thread is 60 degrees.
Thread taper, is 3⁄4 inch per foot.

All units are in inches.

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