Jam nuts are thin hex nut that can be threaded onto a bolt and run tight against the standard nut which will lock the nut in place and prevent it from backing off. This stops an object from being able to thread any further, locking it into place without running up against the connected object. A jam nut is used under a standard nut to create a locking action and in situations where there is not enough bolt thread exposed for a standard hex nut to fit. A common use is of jam nuts are to stop a tie rod end from threading too far into the sleeve. They are also used as lock nuts for adjustable toe stops on roller skates.
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