Specifications of International Thread Standards

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 DiameterMajor Diameter
mm
Major Diameter
Inch
Tapping
Drill Size
mm
TPIPitch
mm
1/8" - 27 NPSM10.2870.4059.246270.941
1/4" - 18 NPSM13.7160.54012.217181.411
3/8" - 18 NPSM17.1450.67515.545181.411
1/2" - 14 NPSM21.3360.84019.279141.814
3/4" - 14 NPSM26.6701.05024.638141.814
1" - 11 1/2 NPSM33.4011.31530.75911.52.209
1 1/4" - 11 1/2 NPSM42.1641.66039.49711.52.209
1 1/2" - 11 1/2 NPSM48.2601.90045.56811.52.209
2" - 11 1/2 NPSM60.3252.37557.60711.52.209
2 1/2" - 8 NPSM73.0252.87569.26683.175
3" - 8 NPSM88.9003.50085.16683.175
3 1/2" - 8 NPSM101.6004.00097.73983.175
4" - 8 NPSM114.3004.500110.38883.175
5" - 8 NPSM141.3005.563137.36383.175
6" - 8 NPSM168.2756.625164.18683.175
NPSM