It is CNC machined from aircraft quality billet 6061 T-6 aluminum. The seal surface portion is made of heat-treated chromoly steel, which is nickel plated and unique to RPM. This steel surface is far superior to our competitor’s aluminum surface, which can become grooved by the seal’s abrasion with dirt and grit potentially contaminating the bearings and leading to premature bearing failure. New sprocket hardware included with race sprocket hubs Honda 400 EX Sprocket Hubs will only fit the RPM Dominator II axle. Will not fit a stock Honda OEM axle.