Bottom brackets at cheap prices from starbike.com
The bottom bracket consists of an axle surround by bearings and is threaded or pressed into the bottom bracket shell of the frame.
Most current crank arms have an integrated bottom bracket axle. This design has replaced older bottom bracket systems with square taper or splined interfaces.
While choosing the bottom bracket, sufficient qualitity of the bearings and seals should be kept in mind. Quality manufacturers of bottom brackets are for example Shimano, Campagnolo or tune.
The BB shell in the frame can come in different configurations, like BSA/ITA threads or various different press-fit standards.
Especially the removal of bottom brackets requires special tools. The links to the required tools can be found in the description of the cranks.