Synchronizers are used in manual transmissions (gearboxes) in automobiles built since about 1960 to ease shifting gears by synchronizing the teeth speed prior to engagement. They allow the toothed collar and the gear to be brought to the same rotational speed before the teeth make contact. They consist of a soft metal (usually brass) cone attached to the gear that makes frictional contact with a cone-shaped cavity in the collar before the teeth are engaged.
