Renthal's Twinring Rear Sprocket puts new innovation and engineering into your drivetrain for outstanding durability. What sets Renthal's Twinring sprocket apart is its unique construction combining a 7075 T651 aluminum inner ring, with an electroless nickel coated steel outer sprocket using a wave-patterned interference fit. This design combines the high wear-resistance of steel and the light weight of aluminum to create a sprocket that handles huge amounts of power while weighing half of conventional, all-steel sprockets. The flat-faced design also helps keep weight down while working with the self-cleaning chain grooves to keep the chain free of any abrasive buildup.