Twinring™ Rear Sprocket - 50 Tooth - Black - Inner ring is the same high strength Ultralight™ 7075 T-6 aluminum used for the standard Renthal sprocket - Outer ring is electro-less nickel coated steel for ultimate durability and is designed with the minimum amount of material to keep weight down - The outer ring is expanded at 200°C and then fitted over the inner; this interference fit combined with the wave pattern ensures a permanent bond for the life of the chainwheel - The flat socket head screws add additional strength to the chainwheel during side impacts and eliminates contact with the chain guide - Self cleaning mud grooves between each tooth prevent dirt build upand reduce chainwheel wear and weight - Will outlast a standard all aluminum sprocket by 3 times, yet is much lighter than an all steel rear sprocket