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British Standard Whitworth (BSW) tapping drill sizes.
| Nominal Dia Pitch | Pitch TPI | Tapping drill Dia mm |
|---|---|---|
| 1/8" | 40 | 2.55 |
| 3/16" | 24 | 3.70 |
| 1/4" | 20 | 5.10 |
| 5/16" | 18 | 6.50 |
| 3/8" | 16 | 7.90 |
| 7/16" | 14 | 9.30 |
| 1/2" | 12 | 10.50 |
| 9/16" | 12 | 12.10 |
| 5/8" | 11 | 13.50 |
| 11/16" | 11 | 15.00 |
| 3/4" | 10 | 16.25 |
| 7/8 | 9 | 19.25 |
| 1 | 8 | 22.00 |
| 1.1/8" | 7 | 24.75 |
| 1.1/4" | 7 | 28.00 |
| 1.1/2" | 6 | 33.50 |
| 1.3/4 | 5 | 39.00 |
| 2" | 4.5 | 44.50 |
British Standard Whitworth (BSW) thread.
The BSW thread was developed by and named after Joseph Whitworth in 1841, BSW was the first standardised thread form. Prior to its
development, factories and manufacturers used their own fasteners, which meant that nuts and bolts could only be used in one place as there
was no interchangability.
The BSW thread has an inclusive angle between threads of 55° and is radiused at the root and peak of each thread, reducing the risk of stress
risers.