The dimensions come from Park Tool’s standards guide and the shell chart from Wheels Manufacturing, the US maker of bottom brackets and adapters, cross-checked against Shimano’s Hollowtech II bottom bracket spec sheets (October 2026). The bottom bracket shell is the tube in the frame that holds the crank bearings; its width and inside diameter decide which bottom bracket fits.
Bottom bracket shell dimensions by standard
| Standard | Type | Shell width | Inside diameter | Thread |
|---|---|---|---|---|
| BSA (English) | Threaded | 68 mm (road), 73 mm (mountain), 83 mm (downhill), 100 mm (fat) | 33.6-33.9 mm | 1.37” × 24 TPI, drive side left-hand |
| Italian | Threaded | 70 mm | 35 mm | 36 mm × 24 TPI, both sides right-hand |
| T47 | Threaded | 68, 73, 83 or 100 mm | About 46 mm | M47 × 1.0, drive side left-hand |
| BB86 | Press-fit | 86.5 mm | 41 mm | No |
| BB92 / BB89.5 | Press-fit | 89.5 or 92 mm | 41 mm | No |
| BB30 | Press-fit | 68 mm (road), 73 mm (mountain) | 42 mm | No |
| PF30 | Press-fit | 68 mm (road), 73 mm (mountain) | 46 mm | No |
| BB386EVO | Press-fit | 86.5 mm | 46 mm | No |
| BBright | Press-fit | 79 mm | 42 mm (Direct Fit) or 46 mm (Press Fit) | No |
| Trek BB90 / BB95 | Press-fit | 90.5 / 95.5 mm | 37 mm | No |
TPI means threads per inch. Mountain bike press-fit shells also come in 104.5 and 107 mm (downhill and e-bike) and 121 and 132 mm (fat bike), always with a 41 mm diameter.
Which crank spindle fits each family
Park Tool groups press-fit shells by inside diameter, which is what really matters for the bearing:
| Family | Standards | Crank spindles it accepts |
|---|---|---|
| PF41 | BB86, BB89.5, BB92, BB104.5, BB107 | 24 mm, 28.99 mm (SRAM DUB), 30 mm or stepped 22/24 mm |
| PF42 | BB30, BB30A, BBright Direct Fit | 30 mm natively; 28.99, 24 or 22/24 mm with adapters |
| PF46 | PF30, PF30A, BB386EVO, BBright Press Fit | 30 mm natively; 28.99, 24 or 22/24 mm with adapters |
| BSA and Italian | External threaded cups | 24 mm (Shimano Hollowtech II, BB-R9100 and similar) |
On threaded shells, the spindle size depends on the bottom bracket you buy: Shimano makes its 24 mm Hollowtech II models for 68 and 73 mm BSA and 70 mm Italian. For other spindles, look for a bottom bracket with the same thread designed for that diameter.
How to tell which bottom bracket your bike has
- Check for threads. Remove the cranks and look inside the shell: if you see threads, it’s BSA, Italian or T47; if it’s smooth, it’s press-fit.
- Measure the width of the shell from side to side with calipers, without the cups.
- Measure the inside diameter (without the cups, if it’s press-fit). Wheels Manufacturing stresses measuring: some brands use the same name for different shells, and BB30A or BB30ai are asymmetric versions with their own dimensions.
- Measure the crank spindle: 24 mm (Shimano), 28.99 mm (SRAM DUB) or 30 mm (the BB30 and PF30 size).
If your frame is 68 mm BSA and you run Shimano cranks, any road Hollowtech II bottom bracket will work. If it’s press-fit, check the family first (41, 42 or 46 mm) and then the spindle. Crank length is worked out separately with the crank length calculator, and the names of every part in six languages are in the drivetrain glossary. Before tightening anything, check the bike torque specs.
Frequently asked questions
What is the difference between BB86 and BB92?
Only the shell width: 86.5 mm on road bikes and 89.5 or 92 mm on mountain bikes. Both have a 41 mm inside diameter and use the same press-fit cups for 24 mm spindles, with or without a spacer.
Are BB30 and PF30 the same?
No. Both were designed for 30 mm spindles, but a BB30 shell is 42 mm inside and a PF30 shell is 46 mm, because in PF30 the bearings sit inside a plastic or aluminum cup. A bottom bracket for one won't fit the other.
Which way does a BSA bottom bracket loosen?
The drive-side cup is left-hand threaded: it loosens clockwise. The non-drive cup is a normal thread. T47 works the same way, while on Italian bottom brackets both cups are right-hand threaded.
Which is better, threaded or press-fit?
Neither is better on dimensions alone. A threaded bottom bracket goes in and out with a wrench; a press-fit one is pressed in with a press and depends on the shell having exactly the right tolerance. T47 combines threads with a wide 46 mm shell.