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.
Dimensions
in| Designation | TPI | Major (in) | Pitch Ø (in) | Minor ext (in) | Tap drill (in) |
|---|---|---|---|---|---|
| 1/8-27 NPS | 27 | 0.4051 | 0.3811 | 0.3512 | 0.3681 |
| 1/4-18 NPS | 18 | 0.5402 | 0.5039 | 0.4594 | 0.4843 |
| 3/8-18 NPS | 18 | 0.6748 | 0.639 | 0.5945 | 0.6193 |
| 1/2-14 NPS | 14 | 0.8402 | 0.7937 | 0.7366 | 0.7685 |
| 3/4-14 NPS | 14 | 1.05 | 1.0035 | 0.9465 | 0.9787 |
| 1-11.5 NPS | 11.5 | 1.315 | 1.2587 | 1.189 | 1.228 |
| 1-1/4-11.5 NPS | 11.5 | 1.6598 | 1.6035 | 1.5339 | 1.5732 |
| 1-1/2-11.5 NPS | 11.5 | 1.9 | 1.8437 | 1.774 | 1.813 |
| 2-11.5 NPS | 11.5 | 2.3748 | 2.3185 | 2.2488 | 2.2882 |
| 2-1/2-8 NPS | 8 | 2.8748 | 2.7937 | 2.6937 | 2.75 |
| 3-8 NPS | 8 | 3.5 | 3.4189 | 3.3189 | 3.3748 |
Sizes are nominal bores, not diameters — 1/8 measures 0.4051 in across the thread. Tapered sizes show a dash for tap drill: a taper is cut with a stepped drill, so there is no single drill size to quote.