3/8
For 3/8, thread standard is NPT; threads per inch (tpi) is 18; thread pitch (mm) is 1.4111; major (outside) diameter (mm) is 17.145; thread angle (degrees) is 60, recorded from its source on 2026-08-12.
- Thread standard
- NPT our reading
- Nominal size
- 3/8
- Threads per inch (TPI)
- 18
- Thread pitch (mm)
- 1.4111
- Major (outside) diameter (mm)
- 17.145 verified
- Thread angle (degrees)
- 60 our reading
- Governing standard
- ASME B1.20.1 our reading
Values marked our reading are our classification of what the source says — the source does not print them in those words. The quote below is the evidence for each one; judge it yourself.
What the source says
0.675 | 17.145 |
— en.wikipedia.org, retrieved 2026-08-12
Sources disagree
More than one authority states this, and they do not state the same thing. Both are reproduced with the source each came from — deciding between them is yours, not ours.
Thread pitch (mm)
en.wikipedia.org says thread pitch (mm) is 1.4111, as of 2026-08-12.
0.675 | 17.145 |
https://en.wikipedia.org/wiki/National_pipe_thread
geminivalve.com says thread pitch (mm) is 1.41122, as of 2026-08-12.
3/8 | 18 | 0.05556 | 1.41122 | 0.675 | 17.15
https://www.geminivalve.com/bsp-thread-vs-npt-fitting/
Major (outside) diameter (mm)
en.wikipedia.org says major (outside) diameter (mm) is 17.145, as of 2026-08-12.
0.675 | 17.145 |
https://en.wikipedia.org/wiki/National_pipe_thread
geminivalve.com says major (outside) diameter (mm) is 17.15, as of 2026-08-12.
3/8 | 18 | 0.05556 | 1.41122 | 0.675 | 17.15
https://www.geminivalve.com/bsp-thread-vs-npt-fitting/
trimantec.com says major (outside) diameter (mm) is 17.3, as of 2026-08-12.
-06 (3/8) | 18 | 17.3 | 0.68 | 15.7 | 0.62
Sources
- en.wikipedia.orghttps://en.wikipedia.org/wiki/National_pipe_thread
- geminivalve.comhttps://www.geminivalve.com/bsp-thread-vs-npt-fitting/
- trimantec.comhttps://trimantec.com/blogs/t/thread-identification-guide