Bottom bracket finder

Take the cups out and measure the bare shell. Three numbers identify almost every frame ever made.

How to measure this

3 steps

1Take the cups out

Measure the bare shell, not the cups or the bearings sitting in it. Every number below is of the frame itself.

Shell measurements

Shell type

If you can see threads cut into the shell it is threaded. A smooth bore is press fit.

Shell width

Face to face across the shell, along the axle.

Shell inner diameter

Across the bore. On a threaded shell, measure across the thread crests.

Matches

Match 100%

BSA / English

68 × 34.8 mm

The default for most of cycling history, and the one coming back into fashion because a threaded shell does not creak.

Thread: 1.37" × 24 tpi
Crank spindles that fit: 24 mm · 22 mm · 30 mm

The drive side cup is left-hand threaded — turn it clockwise to remove.

Match 92%

French

68 × 35 mm

Obsolete since the 1980s.

Thread: M35 × 1.0
Crank spindles that fit: Obsolete — no current cranks fit.

Both cups are right-hand threaded. Unlike an English shell, neither side is reversed, which is why Italian shells work loose more readily.

Match 12%

Italian

70 × 36 mm

Largely confined to older Italian road frames.

Thread: M36 × 24 tpi
Crank spindles that fit: 24 mm · 30 mm

Both cups are right-hand threaded. Unlike an English shell, neither side is reversed, which is why Italian shells work loose more readily.

More than one standard shares these measurements. They are genuinely hard to tell apart without knowing the frame — check the manufacturer's own specification.