# 3/4 — Plumbing fitting and pipe thread standards

For 3/4, thread standard is NPT; threads per inch (tpi) is 14; thread pitch (mm) is 1.8143; major (outside) diameter (mm) is 26.6700; thread angle (degrees) is 60, recorded from its source on 2026-08-12.

- **Thread standard:** NPT _(our reading, not quoted from the source)_
- **Nominal size:** 3/4
- **Threads per inch (TPI):** 14
- **Thread pitch (mm):** 1.8143
- **Major (outside) diameter (mm):** 26.6700 _(verified: appears in the quote below)_
- **Thread angle (degrees):** 60 _(our reading, not quoted from the source)_
- **Governing standard:** ASME B1.20.1 _(our reading, not quoted from the source)_

## What the source says

> 1.050 | 26.6700 |

## 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.

### Thread pitch (mm)

en.wikipedia.org says thread pitch (mm) is **1.8143**, as of 2026-08-12.

> 1.050 | 26.6700 |

Source: https://en.wikipedia.org/wiki/National_pipe_thread

geminivalve.com says thread pitch (mm) is **1.81432**, as of 2026-08-12.

> 3/4 | 14 | 0.07143 | 1.81432 | 1.05 | 26.67

Source: https://www.geminivalve.com/bsp-thread-vs-npt-fitting/


### Major (outside) diameter (mm)

en.wikipedia.org says major (outside) diameter (mm) is **26.6700**, as of 2026-08-12.

> 1.050 | 26.6700 |

Source: https://en.wikipedia.org/wiki/National_pipe_thread

geminivalve.com says major (outside) diameter (mm) is **26.67**, as of 2026-08-12.

> 3/4 | 14 | 0.07143 | 1.81432 | 1.05 | 26.67

Source: https://www.geminivalve.com/bsp-thread-vs-npt-fitting/

trimantec.com says major (outside) diameter (mm) is **26.9**, as of 2026-08-12.

> -12 (3/4) | 14 | 26.9 | 1.06 | 24.9 | 0.98

Source: https://trimantec.com/blogs/t/thread-identification-guide


## Source

- https://en.wikipedia.org/wiki/National_pipe_thread
- https://www.geminivalve.com/bsp-thread-vs-npt-fitting/
- https://trimantec.com/blogs/t/thread-identification-guide

Last verified: 2026-08-12. Review by: 2028-08-11.
Part of [Plumbing fitting and pipe thread standards](https://referencesource.org/plumbing-fitting-thread-standards/).