Lock washers are placed between the bolt head, screw head or nut and the surface of anything that is being fastened. The main function of lock washers is to help bolts and screws retain their torque and prevent them from loosening.
There are two basic types of lock washers: spring action and tooth lock washers. Spring action washers are ideal to use on surfaces that are prone to wear. However, the locking mechanism of this type of washer is only activated when the fastener begins to loosen. As its name implies, tooth lock washers have teeth that bite into the bolt or screw head and the surface to create a ratchet action.