1-1/4
For 1-1/4, thread standard is BSP; threads per inch (tpi) is 11; thread pitch (mm) is 2.309; major (outside) diameter (mm) is 41.910; minor diameter (mm) is 38.952, recorded from its source on 2026-08-12.
- Thread standard
- BSP our reading
- Nominal size
- 1-1/4
- Threads per inch (TPI)
- 11 verified
- Thread pitch (mm)
- 2.309 verified
- Major (outside) diameter (mm)
- 41.910 verified
- Minor diameter (mm)
- 38.952 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
1¼ | 11 | 2.309 | 1.479 | 41.910 | 40.431 | 38.952 |
— 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 41.910, as of 2026-08-12.
1¼ | 11 | 2.309 | 1.479 | 41.910 | 40.431 | 38.952 |
https://amesweb.info/Screws/BSP-Thread-Chart.aspx
htsspares.com says major (outside) diameter (mm) is 41.91, as of 2026-08-12.
1-1/4 Inch BSP | 41.91 mm / 1.-1/2" | 11
https://www.htsspares.com/blog/how-to/how-to-measure-your-bsp-fittings
Sources
- amesweb.infohttps://amesweb.info/Screws/BSP-Thread-Chart.aspx
- htsspares.comhttps://www.htsspares.com/blog/how-to/how-to-measure-your-bsp-fittings