Stainless Steel Nylon insert Lock Nuts. These are metric standard Coarse thread and made from A2 (18-8) stainless steel.
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 an M8 screw).