1/4
For 1/4, thread standard is BSP; threads per inch (tpi) is 19; thread pitch (mm) is 1.337; major (outside) diameter (mm) is 13.157; minor diameter (mm) is 11.445, recorded from its source on 2026-08-12.
- Thread standard
- BSP our reading
- Nominal size
- 1/4 verified
- Threads per inch (TPI)
- 19 verified
- Thread pitch (mm)
- 1.337 verified
- Major (outside) diameter (mm)
- 13.157 verified
- Minor diameter (mm)
- 11.445 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
1/4 | 19 | 1.337 | 0.856 | 13.157 | 12.301 | 11.445 |
— 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 13.157, as of 2026-08-12.
1/4 | 19 | 1.337 | 0.856 | 13.157 | 12.301 | 11.445 |
https://amesweb.info/Screws/BSP-Thread-Chart.aspx
htsspares.com says major (outside) diameter (mm) is 13.16, as of 2026-08-12.
1/4 Inch BSP | 13.16 mm / 1/2" | 19
https://www.htsspares.com/blog/how-to/how-to-measure-your-bsp-fittings
trimantec.com says major (outside) diameter (mm) is 13.2, as of 2026-08-12.
-04 (1/4) | 19 | 13.2 | 0.52 | 11.9 | 0.47
Sources
- amesweb.infohttps://amesweb.info/Screws/BSP-Thread-Chart.aspx
- htsspares.comhttps://www.htsspares.com/blog/how-to/how-to-measure-your-bsp-fittings
- trimantec.comhttps://trimantec.com/blogs/t/thread-identification-guide