38T Chainring Steel material high strength and durable Suits for Single speed bicycle and 67891011 Speeds BikeMTB Drop Stop DesignNarrow wide chainning could prevents chain drop from the chainring it is the most advanced tooth profile on the Market making your cycling safer Aluminium Alloy Arm Aluminium alloy arm the length is 170mm Lightweight and rust resistant Weight the net weight of the cranlset and arm is 08KG 176LB