Pipe Thread Sizes
A list of 16 thread sizes are defined by the standards, ranging from 1⁄16 to 6. The size number was originally based on the inner diameter measured in inches of a steel tube for which the thread was intended, but in the modern metric version of the standard, it is simply a size number.
| Dash thread size |
BSP size |
Threads / in |
Pitch (mm) |
Thread major diameter |
A/F (mm) | Gauge length (mm) |
Corresponding pipe | Tapping drill size (mm) |
||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| (mm) | (in) | DN | OD (mm) |
OD (in) |
Thickness (mm) |
BSP.PL (Rp) | BSP.F (G) | |||||||
| / (0.0625) | 28 | 0.907 | 7.723 | 0.304 | 4 | 6.60 | 6.80 | |||||||
| −2 | ⅛ (0.125) | 28 | 0.907 | 9.728 | 0.383 | 15 | 4 | 6 | 10.2 | 0.40 | 2 | 8.60 | 8.80 | |
| −4 | ¼ (0.25) | 19 | 1.337 | 13.157 | 0.518 | 19 | 6 | 8 | 13.5 | 0.53 | 2.3 | 11.50 | 11.80 | |
| −6 | ⅜ (0.375) | 19 | 1.337 | 16.662 | 0.656 | 22/23 | 6.4 | 10 | 17.2 | 0.68 | 2.3 | 15.00 | 15.25 | |
| −8 | ½ (0.5) | 14 | 1.814 | 20.955 | 0.825 | 27 | 8.2 | 15 | 21.3 | 0.84 | 2.6 | 18.75 | 19.00 | |
| −10 | ⅝ (0.625) | 14 | 1.814 | 22.911 | 0.902 | 16 | 2.6 | - | 21.00 | |||||
| −12 | ¾ (0.75) | 14 | 1.814 | 26.441 | 1.041 | 32 | 9.5 | 20 | 26.9 | 1.06 | 2.6 | 24.25 | 24.50 | |
| −16 | 1 | 11 | 2.309 | 33.249 | 1.309 | 43 | 10.4 | 25 | 33.7 | 1.33 | 3.2 | 30.40 | 30.75 | |
| −20 | 1¼ (1.25) | 11 | 2.309 | 41.910 | 1.650 | 53 | 12.7 | 32 | 42.4 | 1.67 | 3.2 | 39.00 | 39.50 | |
| −24 | 1½ (1.5) | 11 | 2.309 | 47.803 | 1.882 | 57 | 12.7 | 40 | 48.3 | 1.90 | 3.2 | 45.00 | 45.00 | |
| −32 | 2 | 11 | 2.309 | 59.614 | 2.347 | 70 | 15.9 | 50 | 60.3 | 2.37 | 3.6 | 56.75 | 57.00 | |
| 2½ (2.5) | 11 | 2.309 | 75.184 | 2.960 | 17.5 | 65 | 76.1 | 3.00 | 3.6 | |||||
| 3 | 11 | 2.309 | 87.884 | 3.460 | 20.6 | 80 | 88.9 | 3.50 | 4 | |||||
| 4 | 11 | 2.309 | 113.030 | 4.450 | 25.5 | 100 | 114.3 | 4.50 | 4.5 | |||||
| 5 | 11 | 2.309 | 138.430 | 5.450 | 28.6 | 125 | 139.7 | 5.50 | 5 | |||||
| 6 | 11 | 2.309 | 163.830 | 6.450 | 28.6 | 150 | 165.1 | 6.50 | 5 | |||||
The major diameter listed is the outer diameter of the external thread. For a taper thread, it is the diameter at the "gauge length" from the small end of the thread. The taper is 1 to 16, meaning that for each 16 units of measurement increase in the distance from the end, the diameter increases by 1 unit of measurement.
Read more about this topic: British Standard Pipe Thread
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