BSF - British Standard Fine
British standard fine thread (BSF) is a fine screw thread alternative to British Standard Whitworth (BSW) thread. It is used for steel bolts and nuts on much British machinery, including automobiles, prior to adoption of the metric standards. For highly stressed conditions, especially in motorcycles, a finer thread, British Standard Cycle (BSC), was used as well.
| Diameter Inches |
T P I | Pitch inches |
Core Diameter |
Tapping Drill Size |
| 3/16 | 32 | 0.0313 | 0.1475 | 5/32
inch (3.97 mm) |
| 7/32 | 28 | 0.0357 | 0.173 | Number
drill 15 (4.6 mm) |
| 1/4 | 26 | 0.0385 | 0.2008 | Number
drill 6 (5.3 mm) |
| 5/16 | 22 | 0.0455 | 0.2543 | 17/64
inch (6.75 mm) |
| 3/8 | 20 | 0.05 | 0.311 | Letter
drill P (8.2 mm) |
| 7/16 | 18 | 0.0556 | 0.3663 | 9.7
mm (0.3819 inch) |
| 1/2 | 16 | 0.0625 | 0.42 | 7/16
inch (11.11 mm) |
| 9/16 | 16 | 0.0625 | 0.4825 | 1/2
inch (12.7 mm) |
| 5/8 | 14 | 0.0714 | 0.5336 | 14mm (0.5512 inch) |
| 11/16 | 14 | 0.0714 | 0.5961 | 15.5
mm (0.6102 inch) |
| 3/4 | 12 | 0.0833 | 0.6432 | 16.75
mm (0.6594 inch) |
| 7/8 | 11 | 0.0909 | 0.7586 | 25/32
inch (19.84 mm) |
| 1 inch | 10 | 0.1 | 0.872 | 22.75
mm (0.8957 inch) |
