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.
Push Nuts for Dolly Wheel Lock Washers, Hard-To-Find Spring Steel Push-On Pus…
Fastener Size 5/8. Oiled Phosphate Finish: Phosphate coatings prevent corrosion on steel parts. It has a strong surface adhesion, preventing wear and improving friction-induced wear. The oil on the pushnuts’ phosphate coating serves as a sealer to ensure the effectiveness of the phosphate’s corrosion-resistant properties.
