Hex Reversible Lock Nuts
Hex reversible lock nuts have a unique design where the threads in the middle of the nut are distorted for better grip on the bolt.  The hex reversible lock nut can be threaded on to the bolt from either end of the nut.  There is typically an indent on the side of the nut to indicate it is a hex reversible lock nut.These nuts hold better than nylon insert lock nuts and have almost three times the strength of regular low-strength lock nuts.