British standard fine thread
Encyclopedia
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.
The table provides BSF sizes, the threads per inch and wrench jaw sizes. The BSC column indicates where BSF and BSC threads match.
If you need to tap new holes, and you wish to stay original BSF taps seem essential. The table also shows suitable drill sizes if matching BSF-sized drills are not available or broken. Uncommon sizes are shown in italics.
British Standard Whitworth
British Standard Whitworth is one of a number of imperial unit based screw thread standards which use the same bolt heads and nut hexagonal sizes, the others being British Standard Fine thread and British Standard Cycle...
(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
British Standard Cycle
British Standard Cycle or is a British Imperial screw thread standard. Unlike other major British imperial thread standards the thread runs at a 60 degrees rather than a 55 degrees angle...
(BSC), was used as well.
The table provides BSF sizes, the threads per inch and wrench jaw sizes. The BSC column indicates where BSF and BSC threads match.
If you need to tap new holes, and you wish to stay original BSF taps seem essential. The table also shows suitable drill sizes if matching BSF-sized drills are not available or broken. Uncommon sizes are shown in italics.
| 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 | ? | 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 | ? | 37.59mm | 1"1/2 | 22.75mm | |
| 1⅛" | 1.13 | ? | 42.42mm | 1"11/16 | ? | |
| 1¼" | 1.25 | ? | 47.24mm | 1"7/8 | ? | |
| 1½" | 1.50 | ? | 56.39mm | 2"1/4 | ? |