The bottom brackets of a mountain bike can be found where the cranks are attached to the frame. The bracket houses the axle assembly as well as the bearings needed for the cranks. In some circles, this part of the bike is referred to as the “hangar”.
Bottom brackets are available in three basic designs; cup and cone, cartridge, and Ashtabula, or one-piece. Each style requires its own particular set of tools in order to disassemble the cranks. If you’re unsure of the type of bracket you have, it is recommended that you consult with your local bike shop.
Bottom brackets also come in different sizes as well. The majority of brackets are made to British/ISO specifications. However, because there are many different available sizes, it is important to know exactly what you require before buying any replacement parts.