ASME B1.20.160° flankpipe thread
National Pipe Straight Threads
The straight (parallel) counterpart of NPT, used with a gasket or an O-ring rather than relying on the taper to seal. Same diameters and thread counts as NPT; the two are not interchangeable on their own. 11 designations are listed here, all quoted in inches.
Dimensions11 sizes
| Designation | TPI | Major (in) | Pitch Ø (in) | Minor ext (in) | Tap drill (in) |
|---|---|---|---|---|---|
| 1/8-27 NPS | 27 | 0.405 | 0.3811 | 0.3512 | 0.368 |
| 1/4-18 NPS | 18 | 0.54 | 0.5039 | 0.4594 | 0.4844 |
| 3/8-18 NPS | 18 | 0.675 | 0.639 | 0.5945 | 0.6194 |
| 1/2-14 NPS | 14 | 0.84 | 0.7937 | 0.7366 | 0.7686 |
| 3/4-14 NPS | 14 | 1.05 | 1.0035 | 0.9465 | 0.9786 |
| 1-11.5 NPS | 11.5 | 1.315 | 1.2587 | 1.189 | 1.228 |
| 1-1/4-11.5 NPS | 11.5 | 1.66 | 1.6035 | 1.5339 | 1.573 |
| 1-1/2-11.5 NPS | 11.5 | 1.9 | 1.8437 | 1.774 | 1.813 |
| 2-11.5 NPS | 11.5 | 2.375 | 2.3185 | 2.2488 | 2.288 |
| 2-1/2-8 NPS | 8 | 2.875 | 2.7937 | 2.6937 | 2.75 |
| 3-8 NPS | 8 | 3.5 | 3.4189 | 3.3189 | 3.375 |
Sizes are nominal bores, not diameters — 1/8 measures 0.405 in across the thread.