Light Hex Nut with a nylon-filled collar at its back end. When the cap screw or bolt reaches the collar, the threads and nylon form a tight, frictional fit, restricting movement of the cap-screw or bolt when it is subjected to vibration. Identical to a standard pattern nylon insert stop nut but not as thick from top to bottom. Thin pattern heavy hex nuts are used when an insufficient number of projecting threads are present to use a full heavy hex nylon insert stop nut. Nylon Insert Lock Nuts have a captive undersized nylon washer that forms a compression grip to prevent loosening and will stay in place anywhere along the threaded length of the mating fastener. The nut spins freely until its nylon insert engages the threads of the mating part. The nuts are temperature limited and may not be used with certain chemicals, but because the nylon washer element tightly conforms to the mating threads, it provides an effective seal.