British Standard Fine
British Standard Fine (BSF) is a screw thread form, as a fine-pitch alternative to British Standard Whitworth (BSW) thread. It was used for steel bolts and nuts on much British machinery, including cars, prior to adoption of Unified, and later Metric, standards. For highly stressed conditions, especially in motorcycles, a finer thread, British Standard Cycle (BSC), was used as well.
BSF was developed by R. E. B. Crompton, and his assistant George Field.[1]
The table provides BSF sizes, the threads per inch and spanner jaw sizes. The BSC column indicates where BSF and BSC threads match.
The table shows suitable tapping drill sizes. Uncommon sizes are shown in italics.
BSF threads use the 55 degree Whitworth thread form.
| fractional inches | decimal inches | thread per inch | BSC match | Jaw mm exact | or ~inch | drill for tap |
|---|---|---|---|---|---|---|
| 3/16 | 0.19 | 32tpi | `= | 8.59mm | 11/32" 6pt | 5/32" |
| 7/32 | 0.22 | 28tpi | ? | ? | 4.6mm | |
| 1/4 | 0.25 | 26tpi | `= | 11.30mm | -- | 5.3mm |
| 5/16 | 0.31 | 22tpi | 13.34mm | 17/32" | 17/64" | |
| 3/8 | 0.375 | 20tpi | 15.24mm | 5/8" | 8.2mm | |
| 7/16 | 0.44 | 18tpi | 18.03mm | -- | 9.7mm | |
| 1/2 | 0.50 | 16tpi | 20.83mm | 13/16 | 7/16" | |
| 9/16 | 0.56 | 16tpi | 23.37mm | 15/16 | 1/2" | |
| 5/8 | 0.63 | 14tpi | 25.65mm | 1" 6pt | 14mm | |
| 11/16 | 0.69 | 14tpi | 27.94mm | 1'1/8" 6pt | 15.5mm | |
| 3/4 | 0.75 | 12tpi | 30.48mm | 1"1/4 6pt | 16.75mm | |
| 7/8 | 0.88 | 11tpi | 33.02mm | 1"5/16 | 25/32" | |
| 1" | 1.00 | 10tpi | 37.59mm | 1"1/2 | 22.75mm | |
| 1⅛" | 1.13 | 9tpi | 42.42mm | 1"11/16 | 26.50mm | |
| 1¼" | 1.25 | 9tpi | 47.24mm | 1"7/8 | 28.75mm | |
| 1½" | 1.50 | 8tpi | 56.39mm | 2"1/4 | 34.50mm |
References
External links
- Thread sizes
- Jaw sizes for sockets and spanners/wrenches
- Imperial (BSW,BSF,AF) metric conversion charts
- Size comparisons Whitworth/BSF/BA/AF and mm
- Spanner size chart