... :10 Years Buying tipsThe most popular, the low speed, small power, can choose the A3steel Carburizing, quenching,tempering, HRC50 ~ 60 ... have impact load, Teeth more than 25, can choose 35 # steelWith fire, 160 ~ 200HB requirements wear resisting, ... no violent impact, can chose 45 #steel -- sprocket -- Yamaha:AG100,DT100,DT125,DX100, ...