Rear Sprocket. Renthal UltraLight Rear Chainwheels are CNC machined in Manchester, UK from 7075 T6 aluminum to extremely tight tolerances, 66% lighter than steel. Computer engineered and tested to ensure a precise fitment, concentricity and load dispersion with tooth profiling to provide maximum power transfer. With Renthal's combination of high strength base material, cutting edge manufacturing methods and exceptional hardwearing surface treatments its clear to see why Renthal’s light weight all aluminum rear sprockets can be found on the rear wheels of more factory race team machines than all other competing brands combined. Renthal Ultralight™ rear chainwheels are 66% lighter than steel. Precision CNC manufactured to extremely tight tolerances. High-strength specially enhanced 7075 T6 aluminum alloy.