| Standard | Thread | Shell width | Left-hand thread |
|---|---|---|---|
| British (BSA/ISO) | 1.370in × 24 tpi | 68mm standard, 73mm oversize | The fixed (drive-side) cup |
| Raleigh | 1⅜in × 26 tpi | 71mm and 76mm | The fixed cup |
| Italian | 36mm × 24 tpi | 70mm | Neither side |
| French | 35mm × 1mm | 68mm | Neither side |
| Swiss | 35mm × 1mm | 68mm | The fixed cup |
All figures from Sheldon Brown's bottom bracket crib sheet. Raleigh's own 26 tpi threading was used on older Nottingham-built bikes.
Which have you got?
- Measure the shell width68, 70, 71, 73 or 76mm narrows it down straight away.
- Check the thread1.370in is about 34.8mm. Italian is 36mm; French and Swiss are 35mm. Raleigh's 26 tpi is finer than the usual 24 tpi.
- Check the direction of the fixed cupBritish, Raleigh and Swiss fixed cups are left-hand threaded. Italian and French are right-hand.
Reading the markings
This Sakae SR cup is stamped 1.37X24T: a 1.37in thread at 24 threads per inch, the British (BSA/ISO) size in the table above.
Photos: Garry Gregory.
Square taper: JIS and ISO
Square-taper cranks come in two tapers. Sheldon Brown lists Shimano, Sugino (most), SR Sakae, Ritchey and Specialized as JIS, and Campagnolo, older Stronglight, Nervar and TA as ISO. Mixed, the crank sits about 4.5mm out of place: further out with an ISO crank on a JIS spindle, further in with a JIS crank on an ISO spindle. Sheldon Brown says you can often get away with it, but he avoids mixing them, and a JIS crank on an ISO spindle can work its way along the taper with repeated removal.
Chainline
| Set-up | Chainline (Sheldon Brown) |
|---|---|
| Road double | 43.5mm |
| Road triple | 45mm |
| Mountain bike triple | 47.5–50mm |
| Single speed and most hub gears | 40.5–42mm |
Chainline is measured from the frame's centreline to the middle of the chainrings (the middle ring on a triple). The spindle length sets it.
Sources
Checked 19 October 2026. Method tips without a source are our members' experience.