1 ¼
For 1 ¼, thread standard is NPT; threads per inch (tpi) is 11½; major (outside) diameter (mm) is 42.2, recorded from its source on 2026-08-12.
- Thread standard
- NPT our reading
- Nominal size
- 1 ¼ verified
- Threads per inch (TPI)
- 11½ verified
- Major (outside) diameter (mm)
- 42.2 verified
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
-20 (1 ¼) | 11½ | 42.2 | 1.66 | 40.1 | 1.58
— trimantec.com, retrieved 2026-08-12
Source
- trimantec.comhttps://trimantec.com/blogs/t/thread-identification-guide