Plumbing pipe threads and dimensions

BSP thread form stands for British Standard Pipe and is common in Australia and New Zealand. It is based on water flow trade size rather than actual diameter which can lead to some confusion when measuring ports. 

There are two types of BSP threads;
– BSPP – Female & male thread are both parallel
– BSPT – Female thread is parallel and the male thread is tapered.

Both threads have the same pitch, angle (55 degrees) and shape (rounded peaks and valleys).

The below table gives the major and minor diameter for each BSP Trade Thread Size. The minor diameter may be ever so slightly smaller than what is in the table depending upon where it has been manufactured to in the thread gauge.

Trade Size (inch) Threads per inch Pitch Major Diameter Minor Diameter Gage Length
Inch mm Inch mm Inch Mm Inch mm
1/8 28 0.0357 0.907 0.383 9.728 0.3372 8.565 0.1563 3.97
1/4 19 0.0526 1.337 0.518 13.157 0.4506 11.445 0.2367 6.012
3/8 19 0.0526 1.337 0.656 16.662 0.5886 14.95 0.25 6.35
1/2 14 0.0714 1.814 0.825 20.955 0.7336 18.633 0.3214 8.164
3/4 14 0.0714 1.814 1.041 26.441 0.9496 24.12 0.375 9.525
1 11 0.0909 2.309 1.309 33.249 1.1926 30.292 0.4091 10.391
1 ¼ 11 0.0909 2.309 1.65 41.91 1.5336 38.953 0.5 12.7
1 ½ 11 0.0909 2.309 1.882 47.803 1.7656 44.846 0.5 12.7
2 11 0.0909 2.309 2.347 59.614 2.2306 56.657 0.625 15.875
2 ½ 11 0.0909 2.309 2.96 75.184 2.8436 72.227 0.6875 17.463
3 11 0.0909 2.309 3.46 87.884 3.3436 84.927 0.8125 20.638
4 11 0.0909 2.309 4.45 113.03 4.3336 110.073   Â