British Association (BA) Threads Chart
| BASIC DIMENSIONS AND PITCH | |||
|---|---|---|---|
| BA size | Basic major diameter (mm) | Pitch (mm) | Included angle |
| 0 BA | 6.000 | 1.000 | 47.5° |
| 1 BA | 5.400 | 0.900 | 47.5° |
| 2 BA | 4.860 | 0.810 | 47.5° |
| 3 BA | 4.374 | 0.729 | 47.5° |
| 4 BA | 3.937 | 0.656 | 47.5° |
| 5 BA | 3.543 | 0.590 | 47.5° |
| 6 BA | 3.189 | 0.531 | 47.5° |
| 7 BA | 2.870 | 0.478 | 47.5° |
| 8 BA | 2.583 | 0.430 | 47.5° |
| 9 BA | 2.325 | 0.387 | 47.5° |
| 10 BA | 2.092 | 0.349 | 47.5° |
| 11 BA | 1.883 | 0.314 | 47.5° |
| 12 BA | 1.695 | 0.282 | 47.5° |
| 13 BA | 1.525 | 0.254 | 47.5° |
| 14 BA | 1.373 | 0.229 | 47.5° |
| 15 BA | 1.235 | 0.206 | 47.5° |
| 16 BA | 1.112 | 0.185 | 47.5° |
BS 93 defines the basic dimensions for sizes 0 BA through 16 BA. The dimensions follow the BA progression D = 6 × 0.9ⁿ mm and P = 1 × 0.9ⁿ mm, where n is the BA size number.