# 4 — Plumbing fitting and pipe thread standards

For 4, thread standard is BSP; threads per inch (tpi) is 11; thread pitch (mm) is 2.309; major (outside) diameter (mm) is 113.030; minor diameter (mm) is 110.072, recorded from its source on 2026-08-12.

- **Thread standard:** BSP _(our reading, not quoted from the source)_
- **Nominal size:** 4 _(verified: appears in the quote below)_
- **Threads per inch (TPI):** 11 _(verified: appears in the quote below)_
- **Thread pitch (mm):** 2.309 _(verified: appears in the quote below)_
- **Major (outside) diameter (mm):** 113.030 _(verified: appears in the quote below)_
- **Minor diameter (mm):** 110.072 _(verified: appears in the quote below)_
- **Thread angle (degrees):** 55 _(our reading, not quoted from the source)_
- **Governing standard:** ISO 228-1 _(our reading, not quoted from the source)_

## What the source says

> 4 | 11 | 2.309 | 1.479 | 113.030 | 111.551 | 110.072 |

## 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.

### Major (outside) diameter (mm)

amesweb.info says major (outside) diameter (mm) is **113.030**, as of 2026-08-12.

> 4 | 11 | 2.309 | 1.479 | 113.030 | 111.551 | 110.072 |

Source: https://amesweb.info/Screws/BSP-Thread-Chart.aspx

geminivalve.com says major (outside) diameter (mm) is **113.03**, as of 2026-08-12.

> 4 | 11 | 0.0909 | 2.309 | 4.45 | 113.03 | 4.3336 | 110.073 | N/A | N/A

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


### Minor diameter (mm)

amesweb.info says minor diameter (mm) is **110.072**, as of 2026-08-12.

> 4 | 11 | 2.309 | 1.479 | 113.030 | 111.551 | 110.072 |

Source: https://amesweb.info/Screws/BSP-Thread-Chart.aspx

geminivalve.com says minor diameter (mm) is **110.073**, as of 2026-08-12.

> 4 | 11 | 0.0909 | 2.309 | 4.45 | 113.03 | 4.3336 | 110.073 | N/A | N/A

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


## Source

- https://amesweb.info/Screws/BSP-Thread-Chart.aspx
- https://www.geminivalve.com/bsp-thread-vs-npt-fitting/

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/).