Threads per inch, pitch and diameter for the two thread standards used on TUPY Brazil pipe fittings: BSP (British Standard Pipe, 55° Whitworth form to ISO 228 / ISO 7) and NPT (American, 60° form to ASME B1.20.1). To tell a taper thread from a parallel one and identify a size with a caliper, see the BSP thread identification guide.
| Size | TPI | Pitch (mm) | Major dia (mm) |
|---|---|---|---|
| 1/8″ | 28 | 0.907 | 9.73 |
| 1/4″ | 19 | 1.337 | 13.16 |
| 3/8″ | 19 | 1.337 | 16.66 |
| 1/2″ | 14 | 1.814 | 20.96 |
| 3/4″ | 14 | 1.814 | 26.44 |
| 1″ | 11 | 2.309 | 33.25 |
| 1.1/4″ | 11 | 2.309 | 41.91 |
| 1.1/2″ | 11 | 2.309 | 47.80 |
| 2″ | 11 | 2.309 | 59.61 |
| 2.1/2″ | 11 | 2.309 | 75.18 |
| 3″ | 11 | 2.309 | 87.88 |
| 4″ | 11 | 2.309 | 113.03 |
| 5″ | 11 | 2.309 | 138.43 |
| 6″ | 11 | 2.309 | 163.83 |
Nominal reference values. BSP to ISO 228-1; NPT to ASME B1.20.1. Confirm critical dimensions against the current standard.
BSP and NPT look similar but are not interchangeable: the thread angle (55° vs 60°) and the threads per inch differ at most sizes, so forcing one into the other damages the thread and leaks. TUPY supplies fittings in both BSP and NPT - state which you need when you request a quote. For weights and carton quantities use the fitting weight calculator; for the full figure and size range see all fittings.
Pitch in mm = 25.4 / threads per inch. The values that occur on pipe threads:
| TPI | Pitch (mm) | Used on |
|---|---|---|
| 28 | 0.907 | BSP 1/8″ |
| 27 | 0.941 | NPT 1/8″ |
| 19 | 1.337 | BSP 1/4″, 3/8″ |
| 18 | 1.411 | NPT 1/4″, 3/8″ |
| 14 | 1.814 | BSP / NPT 1/2″, 3/4″ |
| 11.5 | 2.209 | NPT 1″ - 2″ |
| 11 | 2.309 | BSP 1″ - 6″ |
| 8 | 3.175 | NPT 2.1/2″ - 4″ |
11 threads per inch, a pitch of 2.309 mm, in the 55° Whitworth form to ISO 228.
BSP is a 55° Whitworth form (ISO 228 / ISO 7); NPT is a 60° form (ASME B1.20.1). The TPI differs at most sizes, so they are not interchangeable.
14 TPI, pitch 1.814 mm, on a pipe outside diameter of 21.34 mm.
