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Fixed Cup
From WikiPedalia
In a conventional threaded bottom bracket, the left cup is adjustable, and its position is secured by a lockring. The right cup is not adjustable, its position is fixed, usually by a shoulder which presses against the side of the bottom-bracket shell. The fixed cup is screwed all the way into the bottom bracket, until the shoulder stops it.
The fixed cup usually has a left-hand thread to prevent it from coming unscrewed due to the action of pedaling.
Bicycles with French or Italian threading have right-hand threaded fixed cups; these fixed cups must be tightened very firmly to keep them in position. Using blue (removable) thread-locking compound also is a good idea.
