Keys and key stock are small metal bars or wedges that fit between an output shaft and the hub of a pulley, gear, sprocket, or other rotating component. They provide the torque to drive the rotating component and help prevent unwanted slipping or movement. Machine keys are pre-cut lengths of metal that insert into the groove of a drive shaft and transfer their rotational force. Key stock consists of long bars of key material that can be cut to length for different applications.