Inner ring is high strength Ultralight 7075 T6 aluminum Outer ring is electroless nickel coasted steel Outer is expanded at 200�C and then fitted to inner, creating a permanent bond for the life of the sprocket The longest lasting most durable offroad sprocket you can buy developed over 5 years The unique flat face design keeps weight to a minimum and means the TwinRing is as narrow as a regular chainwheel Precision CNC machined to extremely tight tolerances Available for most popular dirt bikes with 520 chain sizes ranging from 47-53 �