Renthal Front Sprocket 289 / 520 [Yamaha]Renthal sprockets are simply the finest sprockets on the market today. Their sprocket features a specially developed nickel chrome molybdenum steel which is case hardened and core refined to give the ultimate combination of strength and hardness. Grooved sprockets have cut outs at the bottom of the tooth to allow the escape of mud that would otherwise be trapped between the chainwheel and the chain. Allowing the easy escape of the mud prevents tension