NPT thread, nominal size 1/8 — dimensions
For NPT thread, nominal size 1/8, threads per inch (tpi) is 27; thread pitch (mm) is disputed: 0.9407 per en.wikipedia.org, 0.94082 per geminivalve.com; major (outside) diameter (mm) is disputed: 10.287 per en.wikipedia.org, 10.29 per geminivalve.com, 10.3 per trimantec.com; thread angle (degrees) is 60; governing standard is ASME B1.20.1, recorded from its source on 2026-08-12.
- Thread standard
- NPT our reading
- Nominal size
- 1/8
- Threads per inch (TPI)
- 27
- Thread pitch (mm)
- 0.9407 sources disagree
- Major (outside) diameter (mm)
- 10.287 sources disagree
- 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
0.405 | 10.287 |
— 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 0.9407, as of 2026-08-12.
0.405 | 10.287 |
https://en.wikipedia.org/wiki/National_pipe_thread
geminivalve.com says thread pitch (mm) is 0.94082, as of 2026-08-12.
1/8 | 27 | 0.03704 | 0.94082 | 0.405 | 10.29
https://www.geminivalve.com/bsp-thread-vs-npt-fitting/
Major (outside) diameter (mm)
en.wikipedia.org says major (outside) diameter (mm) is 10.287, as of 2026-08-12.
0.405 | 10.287 |
https://en.wikipedia.org/wiki/National_pipe_thread
geminivalve.com says major (outside) diameter (mm) is 10.29, as of 2026-08-12.
1/8 | 27 | 0.03704 | 0.94082 | 0.405 | 10.29
https://www.geminivalve.com/bsp-thread-vs-npt-fitting/
trimantec.com says major (outside) diameter (mm) is 10.3, as of 2026-08-12.
-02 (1/8) | 27 | 10.3 | 0.41 | 9.4 | 0.37
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