British Standard Cycle Thread (BSC)
A thread invented for bicycles, and still on them.
Origin
Developed by the British cycle industry in the 1880s and 1890s, when Coventry and Birmingham were building bicycles faster than anywhere on earth.
The catch
Whitworth was too coarse for thin-walled cycle tubing, which would simply tear. So the trade cut a finer thread at a sharper 60-degree angle, settling on 26 threads per inch for most small fittings regardless of diameter and 24 for the large bearing cups. The British bottom bracket, 1.370 inches at 24 threads with a left-hand thread on the drive side, is why it still will not accept an Italian one, which is right-handed on both sides and a slightly different diameter.
| Component | Size | Threads per inch | Still current? |
|---|---|---|---|
| Bottom bracket (British) | 1.370 in | 24 | Yes, the world standard |
| Headset | 1.000 in | 24 | On older frames |
| Pedal | 9/16 in | 20 | Yes, universal |
| Freewheel | 1.370 in | 24 | On older hubs |
| Seat pin bolt | 1/4 in | 26 | Largely superseded |
| Spoke nipple | 14 gauge (2 mm) spoke | 56 | Yes, in traditional wheels |
The British cycle industry was for a period the largest in the world, and the standards it set outlived it comprehensively. The British bottom bracket thread is now the international norm, fitted to bicycles built in countries whose own cycle industries never used BSC for anything else. It is a rare case of a British standard winning globally not through empire or legislation but simply because enough bicycles were built to it.