Metric Nylon Insert Lock Nuts (DIN 985), Class 10 Zinc

METRIC CLASS 10 NYLON INSERT THIN LOCKNUT, ZINC CR+3

Metric nylon inset lock nuts are basically a hex nut with a nylon-filled collar at its back end. When a screw reaches the collar, the threads and nylon form a tight, frictional fit, restricting movement of the screw when it's subject to vibration.