Ultralight Rear Sprocket Black 404U-525-42P-HA Manufactured to extremely tight tolerances. 7075-T6 aluminum alloy rear chainwheels are 66% lighter than steel, yet incredibly durable. Advanced tooth profile, concentricity and accuracy of fit provide maximum power transfer and long-life. The combination of a very high-strength base material and an exceptionally hard-wearing surface results in significantly increased chainwheel life. Most available in ultralight design. Hard anodized finish for better wear resistance.