How to Buy an External Bottom Bracket

So you've followed Step 1 of our how to buy a bottom bracket article, and you've determined you needed an external bottom bracket. Let's keep moving in the selection of the proper external bottom bracket.

Step 2: Selecting the type of bottom bracket interface

All types of external bottom brackets are not interchangeable - you need to select an external bottom bracket with the proper interface required to install your crankset. Here are the most common types of spindle interfaces for external crankset (note that this is not a complete list).

Hollowtech II


Compatible with Shimano cranksets designed for Hollowtech II.

Cranksets feature a 24mm spindle attached to the drive side.



Giga-X-Pipe (GXP) compatible with Truvativ and Sram cranksets designed for GXP.

Cranksets feature a 24 to 22mm tapered spindle attached to the drive side.




         MegaExo Light




         MegaExo Quad

The MegaExo interface features a 24mm spindle attached to the drive side of the crankset.

Each variation of MegaExo is designed to work with specific FSA crankset.

Step 3: Selecting the bottom bracket shell width

External bottom brackets are designed to fit bottom bracket shells of specific widths. Some bottom brackets can fit multiple shell widths by using purpose build spacers (for example a 68mm and a 73mm shell), while others are designed to only work with a single shell width. In order to select the proper bottom bracket, simply measure the width of your bottom bracket shell and select a compatible bottom bracket.



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