# 3/4 — Plumbing fitting and pipe thread standards For 3/4, thread standard is BSPT; threads per inch (tpi) is 14; thread pitch (mm) is 1.814; major (outside) diameter (mm) is 26.44; minor diameter (mm) is 24.12, recorded from its source on 2026-08-12. - **Thread standard:** BSPT _(our reading, not quoted from the source)_ - **Nominal size:** 3/4 _(verified: appears in the quote below)_ - **Threads per inch (TPI):** 14 _(verified: appears in the quote below)_ - **Thread pitch (mm):** 1.814 _(verified: appears in the quote below)_ - **Major (outside) diameter (mm):** 26.44 _(verified: appears in the quote below)_ - **Minor diameter (mm):** 24.12 _(verified: appears in the quote below)_ - **Thread angle (degrees):** 55 _(our reading, not quoted from the source)_ - **Governing standard:** ISO 7-1 _(our reading, not quoted from the source)_ ## What the source says > BSPT R 3/4 | 3/4" | 14 | 1.814 | 9.5 | 1.0 / 1.8 | 26.44 | 25.28 | 24.12 | 0 | -999.00 | R | BSPT R 1 | 1" | 11 | 2.309 | 10.4 | 1.0 / 2.3 | 33.25 | 31.77 | 30.29 | 0 | -999.00 | R | BSPT R 1 1/4 | 1 1/4" | 11 | 2.309 | 12.7 | 1.0 / 2.3 | 41.91 | 40.43 | 38.95 | 0 | -999.00 | R | BSPT R 1 1/2 | 1 1/2" | 11 | 2.309 | 12.7 | 1.0 / 2.3 | 47.80 | 46.32 | 44.85 | 0 | -999.00 | R | BSPT R 2 | 2" | 11 | 2.309 | 15.9 | 1.0 / 2.3 | 59.61 | 58.14 | 56.66 | 0 | -999.00 | R | BSPT R 2 1/2 | 2 1/2" | 11 | 2.309 | 17.5 | 1.5 / 3.5 | 75.18 | 73.71 | 72.23 | 0 | -999.00 | R | BSPT R 3 | 3" | 11 | 2.309 | 20.6 | 1.5 / 3.5 | 87.88 | 86.41 | 84.93 | 0 | -999.00 | R | BSPT R 4 | 4" | 11 | 2.309 | 25.4 | 1.5 / 3.5 | 113.03 | 111.55 | ## Source - https://www.machiningdoctor.com/charts/bsp/ 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/).