Bottom Bracket Shell. 68,BSA
The Bottom bracket shell is the part of the frame that holds the crank bearings. Three key items are Width, Diameter and Threading. Diameter and Threading are almost always BSA (British standard). The width is most commonly 68mm, but there are some that are 70 or 73. For purposes of compact reports, the width and threading are combined. Example: 68,BSA or 73,BSA, or PressFit
- In the above, 68 is the Width, and BSA tells you both the diameter and threads.
See tables at the following:
ShellType ShellD Width Thread -------------------------------------
BSA 24 68
Mega Exo 24 68
386 EVO 46
BB Bearing type
- A BB bearing type requires a certain shell type
- A Crank model requires a certain BB Bearing type (Sq Taper cartridge)
A shell t
- the inner spindle diameter is a characteristic of the crank, not the shell. The crank spindle most definitely expects bearings of a certain size and spacing. It will require a certain type of shell
Some carbon frames now are designed to have the bearings "press fitted" into the frame. These bikes follow a different standard. See separate document.
The common threaded bottom bracket uses cups or adaptors with the thread specification of 1.37" x 24 threads per inch (approximately 34.8mm diameter). The most commonly used term for this standard is "English" threading, sometimes abbreviated as ENG. Also known as "BSA" or Standard threaded. BSA means "British Standard