NPSM Pipe Thread ANSI B 1.20.1-1983 (R1992)

Parallel pipe thread for mechanical joints, not self-sealing. While external and internal tapered pipe threads for joints can be used for all purposes, there are also mechanical joints where parallel threads work better. They are used in pipes of iron, steel and brass where there is no internal pressure. (National Pipe Straight Mechanical), formerly known as NPS. The flank angle is 60°, the profile was originated by William Sellers.

Nominal Diameter Major Diameter
mm
Major Diameter
Inch
Tapping
Drill Size
mm
TPI Pitch
mm
1/8" - 27 NPSM 10.287 0.405 10.084 27 0.941
1/4" - 18 NPSM 13.716 0.540 13.360 18 1.411
3/8" - 18 NPSM 17.145 0.675 16.815 18 1.411
1/2" - 14 NPSM 21.336 0.840 20.904 14 1.814
3/4" - 14 NPSM 26.670 1.050 26.264 14 1.814
1" - 11 1/2 NPSM 33.401 1.315 32.842 11.5 2.209
1 1/4" - 11 1/2 NPSM 42.164 1.660 41.605 11.5 2.209
1 1/2" - 11 1/2 NPSM 48.260 1.900 47.676 11.5 2.209
2" - 11 1/2 NPSM 60.325 2.375 59.715 11.5 2.209
2 1/2" - 8 NPSM 73.025 2.875 72.161 8 3.175
3" - 8 NPSM 88.900 3.500 88.062 8 3.175
3 1/2" - 8 NPSM 101.600 4.000 100.787 8 3.175
4" - 8 NPSM 114.300 4.500 113.436 8 3.175
5" - 8 NPSM 141.300 5.563 140.411 8 3.175
6" - 8 NPSM 168.275 6.625 167.259 8 3.175