Dimension table
| Designation | TPI | Nom. OD (mm) | Pitch (mm) | d₂ (mm) | D₁ (mm) |
|---|---|---|---|---|---|
| G 1/16 | 28 | 7.723 | 0.907 | 7.142 | 6.562 |
| G 1/8 | 28 | 9.728 | 0.907 | 9.147 | 8.567 |
| G 1/4 | 19 | 13.157 | 1.337 | 12.301 | 11.445 |
| G 3/8 | 19 | 16.662 | 1.337 | 15.806 | 14.950 |
| G 1/2 | 14 | 20.955 | 1.814 | 19.794 | 18.633 |
| G 5/8 | 14 | 22.911 | 1.814 | 21.750 | 20.589 |
| G 3/4 | 14 | 26.441 | 1.814 | 25.280 | 24.119 |
| G 7/8 | 14 | 30.201 | 1.814 | 29.040 | 27.879 |
| G 1 | 11 | 33.249 | 2.309 | 31.770 | 30.291 |
| G 1-1/8 | 11 | 37.897 | 2.309 | 36.418 | 34.939 |
| G 1-1/4 | 11 | 41.910 | 2.309 | 40.431 | 38.952 |
| G 1-3/8 | 11 | 44.323 | 2.309 | 42.844 | 41.365 |
| G 1-1/2 | 11 | 47.803 | 2.309 | 46.324 | 44.845 |
| G 1-3/4 | 11 | 53.746 | 2.309 | 52.267 | 50.788 |
| G 2 | 11 | 59.614 | 2.309 | 58.135 | 56.656 |
| G 2-1/2 | 11 | 75.184 | 2.309 | 73.705 | 72.226 |
| G 3 | 11 | 87.884 | 2.309 | 86.405 | 84.926 |
| G 4 | 11 | 113.030 | 2.309 | 111.551 | 110.072 |
| G 5 | 11 | 138.430 | 2.309 | 136.951 | 135.472 |
| G 6 | 11 | 163.830 | 2.309 | 162.351 | 160.872 |
Source: ISO 228-1:2003. Nom. OD = thread outer diameter (crest). Whitworth 55° formulas: d₂ = d − 0.6403×P · D₁ = d − 1.2806×P. Values rounded to 3 decimal places.
Key technical characteristics
- Flank angle
- 55° (Whitworth)
- Profile
- Parallel (no taper)
- Standard
- ISO 228-1
- Designation
- G + size (e.g. G ½)
- Sealing mechanism
- Flat washer or o-ring (face seal)
- Rounded roots
- Yes — Whitworth profile
Typical applications
- European and Asian hydraulic and pneumatic equipment (common in Japanese machines).
- Pipe fittings in Fanuc, Mazak, DMG Mori and other European/Asian machine tools.
- Coolant connections in imported machining centers.
- Compressed air systems in plants following BSP standards.
Compatibility and interoperability
- ✗NOT compatible with NPT — different angle (55° vs 60°) and BSPP is parallel while NPT is tapered.
- ✗NOT interchangeable with BSPT (R) — both are BSP but BSPP is parallel and BSPT is tapered. The sealing mechanism is completely different.
- ✓BSPP female may accept BSPT male in some manufacturers — but sealing depends on the face o-ring, not the male taper. Verify with fitting manufacturer.
Selection guide
- 01Identify BSPP (G) by the washer or o-ring at the fitting face — if absent, it is likely BSPT or NPT.
- 02For high pressures (>200 bar) prefer face o-ring over flat washer — better seal integrity.
- 03Nominal size G ½ does NOT indicate actual ½ inch diameter — it is the nominal pipe number.
- 04In Japanese machinery, BSPP often coexists with metric threads — verify with the machine manual.