The common shell standards
The shell is the part of the frame the bottom bracket fits into. It's either threaded (the bearings screw in) or press-fit (the bearings are pressed in).
| Standard | Shell width | Bore / thread | Type |
|---|---|---|---|
| BSA (English) | 68mm road, 73mm MTB | 1.37" × 24tpi | Threaded |
| Italian | 70mm | 36mm × 24tpi | Threaded |
| T47 | 68mm or 86.5mm | 47mm thread | Threaded |
| BB86 | 86.5mm | 41mm | Press-fit |
| BB92 | 89.5mm | 41mm | Press-fit |
| BB30 | 68mm | 42mm | Press-fit (bearings direct in frame) |
| PF30 | 68mm | 46mm | Press-fit |
| BB386EVO | 86.5mm | 46mm | Press-fit |
Match it to your spindle
A bottom bracket is made for a shell and a spindle. For example, a BSA bottom bracket for a Shimano 24mm spindle won't fit a SRAM DUB crank. Check your chainset's spindle in the Chainsets and chainrings guide, then pick the bottom bracket for both.
How to work out what you have
- Look for threads. Remove the cranks. If you can see cups screwed into the frame, it's threaded.
- Measure the shell width across the frame, from one face of the shell to the other.
- Measure the bore (inside diameter) on press-fit frames, with the bearings removed.
- Check the frame maker's spec sheet. It's often the quickest answer.
Signs it needs replacing
- Creaking when you pedal hard
- Play when you rock the cranks side to side
- Rough or gritty feeling when you spin the cranks by hand
Creaks can also come from pedals, chainring bolts or the saddle, so rule those out first.
FAQs
Can I swap press-fit for threaded?
Not on the same frame, but some threaded-style press-fit bottom brackets screw together inside the shell and can creak less.
Do I need special tools?
Yes. Threaded bottom brackets need the right splined tool, and press-fit ones need a bearing press and removal tool.
Which is better?
Threaded is easier to service at home. Press-fit can be lighter and stiffer but needs a precise fit.