Metric Nylon insert Lock Nuts. Class 8 Steel with Black Oxide coating.
Nylon insert nuts are hex nuts with a built in nylon ring to resist loosening and vibration. These are commonly known as nyloc nuts. When a threaded fastener reaches the collar, the threads and nylon form a tight, compressive force.
Nut Size is the size of the screw that the nut is for (Example: M8 nut for a M8 screw).