BSPP (G) Thread Chart (Printable)
Threads per inch and major outside diameter for BSPP G sizes 1/8″ through 2″ per ISO 228-1 — parallel threads that seal on a face, washer or gasket, never on the thread itself.
G sizes, TPI and major diameter
| BSPP size | Threads per inch | Major OD (mm) |
|---|---|---|
| G1/8 | 28 | 9.728 |
| G1/4 | 19 | 13.157 |
| G3/8 | 19 | 16.662 |
| G1/2 | 14 | 20.955 |
| G3/4 | 14 | 26.441 |
| G1 | 11 | 33.249 |
| G1-1/4 | 11 | 41.910 |
| G1-1/2 | 11 | 47.803 |
| G2 | 11 | 59.614 |
How to use this chart
G threads are parallel — the flanks do not wedge as the joint tightens — so the seal comes from a washer, O-ring, bonded seal or a machined face, not from the thread. That is the practical difference from NPT on the bench: an NPT joint seals with tape or dope on tapered flanks, a G joint needs its sealing element seated. Dimensions follow ISO 228-1 published values; the standard governs for gauge decisions.
From our guide: NPT vs G (BSP) threads. State G-thread sizes as "G1/2" plus the sealing element on theRFQ.