• The longest lasting most durable off-road sprocket you can buy developed over 5 years. • The unique flat face design keeps weight to a minimum and means the TwinRing's as narrow as a regular chainwheel. • Inner Ring is high strength Ultralight 7075 T6 Aluminium. Outer Ring is Electroless Nickel Coated steel. • Outer is expanded at 200 °C and then fitted to inner, creating a permanent bond for the life of the sprocket. Generic Image used.