NPT Thread Sizes
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