Whitworth & British
BA British Association Thread
Small metric-based threads numbered 0 BA (largest) to 25 BA, historically used in electrical equipment and instruments.
- Standard
- BS 93
- Flank angle
- 47.5°
- Sizes listed
- 26
- Range
- BA No. 0 – BA No. 25
| BA Thread No. | Diameter mm | Tapping Drill Size mm | Pitch mm |
|---|---|---|---|
| BA No. 0 | 6.00 | 4.80 | 1.00 |
| BA No. 1 | 5.30 | 4.22 | 0.90 |
| BA No. 2 | 4.70 | 3.73 | 0.81 |
| BA No. 3 | 4.10 | 3.22 | 0.73 |
| BA No. 4 | 3.60 | 2.81 | 0.66 |
| BA No. 5 | 3.20 | 2.49 | 0.59 |
| BA No. 6 | 2.80 | 2.16 | 0.53 |
| BA No. 7 | 2.50 | 1.92 | 0.48 |
| BA No. 8 | 2.20 | 1.68 | 0.43 |
| BA No. 9 | 1.90 | 1.43 | 0.39 |
| BA No. 10 | 1.70 | 1.28 | 0.35 |
| BA No. 11 | 1.50 | 1.13 | 0.31 |
| BA No. 12 | 1.30 | 0.96 | 0.28 |
| BA No. 13 | 1.20 | 0.90 | 0.25 |
| BA No. 14 | 1.00 | 0.72 | 0.23 |
| BA No. 15 | 0.90 | 0.65 | 0.21 |
| BA No. 16 | 0.79 | 0.65 | 0.19 |
| BA No. 17 | 0.70 | 0.50 | 0.17 |
| BA No. 18 | 0.62 | 0.44 | 0.15 |
| BA No. 19 | 0.54 | 0.37 | 0.14 |
| BA No. 20 | 0.48 | 0.34 | 0.12 |
| BA No. 21 | 0.42 | 0.29 | 0.11 |
| BA No. 22 | 0.37 | 0.25 | 0.098 |
| BA No. 23 | 0.33 | 0.22 | 0.090 |
| BA No. 24 | 0.29 | 0.19 | 0.080 |
| BA No. 25 | 0.25 | 0.16 | 0.072 |
Reference values only. Verify against the current edition of the governing standard before use in production drawings or manufacturing. Provided by Micro Components as a free engineering resource.