There is actually the following ingenious design: the sprocket has a spring-held card inside, the card has a string or a string of steel balls, they are controlled in a ratchet chute, when the rear sprocket rotates forward, the steel ball will roll in the chute to the narrower side; and the backward rotation of the steel ball will roll in a wider direction, this design can ensure that when the chain advances, the rear sprocket will be stuck to drive the rear wheel to rotate, when the chain is stationary or backward when the rear chain does not move, but does not affect the free rotation of the wheel.
This device, commonly known as the "kowtow worm", is an important part of the bicycle hub (commonly known as the tower base), which is a ratchet mechanism that can only rotate in one direction and will lock in r e v e r s e.
Bicycle Trivia (6) - Only inlet and not exhale the valve core and epilogue
Bicycle Trivia (4) -The chain drive of the bicycle and its transmission principle
Bicycle Trivia (3) - Flywheel
Bicycle Trivia (2) - Small steel balls have a big role
