DESCRIPTION - Black Luster® Steel Nylon Insert Jam Lock Nuts are thinner than regular lock nuts and provide best in class decorative appearance and better corrosion resistance than black oxide and zinc plated finishes. Resistant to 1,000 hours of salt spray per ASTM B117*. Nylon Insert Lock Nuts have a nylon insert that lines a portion of threads inside the nut. The nylon insert locks the nut by applying a compressive force against the screw preventing loosening from vibration.