RENTHAL Rear Sprockets Hard Anodised Rear Chainwheels Renthal's hard anodised rear chainwheels are specifically designed for road and road racing applications. They are CNC machined from the same 7075 T6 material as our offroad chainwheels, yet feature the increased longevity from the hard anodizing process. Hard anodising is an integral surface coating which significantly increases the hardness and wear resistance of the chainwheel surface