Lock washers, push-on nuts, or pushnuts
were first designed to serve as retainers for bolts in car bumpers before the final assembly.
These days, it serves more or less the same function. This 8-pack pushnut serves as both a retainer and fastener for low-torque wheels, providing a balance between strength and durability. As a cost-effective solution, pushnuts provide the same - even superior performance in comparison to other similar fasteners.
The spring force produced by its teeth allows the pushnut to create more friction between itself and the shaft increasing its rotational resistance.
The black coating on these pushnuts is a zinc phosphate coating with an oil sealer. Zinc phosphate coatings strongly adhere to surfaces either through immersion or spray application.