Twin Ring Rear Sprocket. In development for over 5 years, the new Renthal TwinRing sprocket will re-define the term durability in off-road drivetrain products. The longest lasting most durable off-road sprocket you can buy. 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.