3/8
For 3/8, thread standard is BSP; threads per inch (tpi) is 19; thread pitch (mm) is 1.337; major (outside) diameter (mm) is 16.662; minor diameter (mm) is 14.950, recorded from its source on 2026-08-12.
- Thread standard
- BSP our reading
- Nominal size
- 3/8 verified
- Threads per inch (TPI)
- 19 verified
- Thread pitch (mm)
- 1.337 verified
- Major (outside) diameter (mm)
- 16.662 verified
- Minor diameter (mm)
- 14.950 verified
- Thread angle (degrees)
- 55 our reading
- Governing standard
- ISO 228-1 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
3/8 | 19 | 1.337 | 0.856 | 16.662 | 15.806 | 14.950 |
— amesweb.info, 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.
Major (outside) diameter (mm)
amesweb.info says major (outside) diameter (mm) is 16.662, as of 2026-08-12.
3/8 | 19 | 1.337 | 0.856 | 16.662 | 15.806 | 14.950 |
https://amesweb.info/Screws/BSP-Thread-Chart.aspx
geminivalve.com says major (outside) diameter (mm) is 16.662, as of 2026-08-12.
3/8 | 19 | 0.0526 | 1.337 | 0.656 | 16.662 | 0.5886 | 14.95 | 0.25 | 6.25
https://www.geminivalve.com/bsp-thread-vs-npt-fitting/
htsspares.com says major (outside) diameter (mm) is 16.66, as of 2026-08-12.
3/8 Inch BSP | 16.66 mm / 5/8" | 19
https://www.htsspares.com/blog/how-to/how-to-measure-your-bsp-fittings
trimantec.com says major (outside) diameter (mm) is 16.5, as of 2026-08-12.
-06 (3/8) | 19 | 16.5 | 0.65 | 15.2 | 0.60
https://trimantec.com/blogs/t/thread-identification-guide
Minor diameter (mm)
amesweb.info says minor diameter (mm) is 14.950, as of 2026-08-12.
3/8 | 19 | 1.337 | 0.856 | 16.662 | 15.806 | 14.950 |
https://amesweb.info/Screws/BSP-Thread-Chart.aspx
geminivalve.com says minor diameter (mm) is 14.95, as of 2026-08-12.
3/8 | 19 | 0.0526 | 1.337 | 0.656 | 16.662 | 0.5886 | 14.95 | 0.25 | 6.25
Sources
- amesweb.infohttps://amesweb.info/Screws/BSP-Thread-Chart.aspx
- geminivalve.comhttps://www.geminivalve.com/bsp-thread-vs-npt-fitting/
- htsspares.comhttps://www.htsspares.com/blog/how-to/how-to-measure-your-bsp-fittings
- trimantec.comhttps://trimantec.com/blogs/t/thread-identification-guide