There is no standard in bicycle bottom brackets and manufacturers often come up with new designs specific to a brand or model. This creates a lot of confusion for the consumer when they have to replace their bottom bracket. The bottom bracket is the bearing set that allows the crank to spin freely. It has match the diameter of the crank spindle; usually 24mm or 30mm. Beyond that the bottom bracket is specific to the bike design. Before you purchase a bottom bracket visit your manufacturers website to determine the exact specifications of your bicycles' bottom bracket.