BSP thread chart: G pipe thread dimensions to ISO 228-1
Parallel British Standard Pipe threads (G) to ISO 228-1, from G 1/16 to G 4, with threads per inch, pitch and diameters in millimetres.
BSP thread chart: G pipe threads to ISO 228-1
| Size | TPIthreads per inch | Pmm | dmajor, mm | d2pitch diameter, mm | d1minor, mm | Tap drillmm |
|---|---|---|---|---|---|---|
| G 1/16 | 28 | 0.907 | 7.723 | 7.142 | 6.561 | 6.8 |
| G 1/8 | 28 | 0.907 | 9.728 | 9.147 | 8.566 | 8.8 |
| G 1/4 | 19 | 1.337 | 13.157 | 12.301 | 11.445 | 11.8 |
| G 3/8 | 19 | 1.337 | 16.662 | 15.806 | 14.95 | 15.3 |
| G 1/2 | 14 | 1.814 | 20.955 | 19.793 | 18.631 | 19 |
| G 5/8 | 14 | 1.814 | 22.911 | – | 20.587 | 21 |
| G 3/4 | 14 | 1.814 | 26.441 | 25.279 | 24.117 | 24.5 |
| G 7/8 | 14 | 1.814 | 30.201 | – | 27.877 | – |
| G 1 | 11 | 2.309 | 33.249 | 31.77 | 30.291 | – |
| G 1 1/8 | 11 | 2.309 | 37.897 | – | 34.939 | 35.5 |
| G 1 1/4 | 11 | 2.309 | 41.91 | 40.431 | 38.952 | 39.5 |
| G 1 1/2 | 11 | 2.309 | 47.803 | 46.324 | 44.845 | – |
| G 1 3/4 | 11 | 2.309 | 53.746 | – | 50.788 | – |
| G 2 | 11 | 2.309 | 59.614 | 58.135 | 56.656 | – |
| G 2 1/4 | 11 | 2.309 | 65.71 | – | 62.752 | – |
| G 2 1/2 | 11 | 2.309 | 75.184 | 73.705 | 72.226 | – |
| G 3 | 11 | 2.309 | 87.884 | 86.405 | 84.926 | – |
| G 4 | 11 | 2.309 | 113.03 | 111.551 | 110.072 | – |
Dimensions in millimetres. A dash means fewer than two independent sources gave that value.
Sources the values were checked against (7)
- Wikipedia, British Standard Pipe (tabla G/R: TPI, paso, diametros mayor y menor, broca de G al 80 %)
- Machining Doctor, fichas BSPP G (una por medida: TPI, paso, mayor, flancos, menor, broca)
- AmesWeb, BSP Thread Chart (TPI, paso, mayor, flancos, menor)
- Engineering ToolBox, Whitworth Pipe Threads (G: mayor, menor, TPI)
- Engineering ToolBox, BS 21 pressure tight pipe thread (TPI, paso, mayor, menor)
- Tameson, BSP thread (G: mayor, menor, TPI)
- Hartner, Kernlochdurchmesser für das Gewindeschneiden (Rohrgewinde G, DIN 336)
BSP thread dimensions: why 1/2 is not half an inch
The size of a pipe thread refers to the nominal bore of the pipe it was made for, not to the thread itself. A G 1/2 thread is 20.955 mm across the crests, with 14 threads per inch. That is why you cannot measure a pipe thread with a ruler and read the size: measure the major diameter and count the threads, then find the row in the chart.
G thread and R thread
G threads to ISO 228-1 are parallel and do not seal on the thread: the seal is a washer, an O-ring or a flat face. R and Rp threads to ISO 7-1 are tapered or parallel threads that seal on the thread itself with a sealant. They share the major diameter and the number of threads per inch of each size, but not the other diameters, so the values in this chart apply to G threads only.
BSP threads: common questions
- What are the dimensions of a 1/2 BSP thread?
- G 1/2 has 14 threads per inch (1.814 mm pitch), a major diameter of 20.955 mm and a minor diameter of 18.631 mm. The tap drill is 19.0 mm.
- What are the dimensions of a 1/4 BSP thread?
- G 1/4 has 19 threads per inch (1.337 mm pitch), a major diameter of 13.157 mm and a minor diameter of 11.445 mm.