Bottom Bracket

The crankset (chainset) is linked to the cycle by the bottom bracket on a bicycle and allows the crankset to rotate freely. It includes a spindle to which the crankset is attached and bearings that allow rotation of the spindle and cranks. 

To enable you to pedal, your bottom bracket is that hollow bit at the bottom of the frame into which the bike’s cranks fit. There will be an axle in it that turns into a pair of bearings: one on the right-hand side of the bike, the other on the non-drive side of the left-hand side of the bike.

HOLLOW TECH BB 51 – BOTTOM BRACKET