Renthal Sprockets Kit - Grooved Front Countershaft Sprocket & Blue Ultralight Rear Sprocket. GROOVED FRONT COUNTERSHAFT SPROCKET. Renthal Front Chainwheels are simply the finest front chainwheel on the market today. Their Front Chainwheels feature a specially developed Nickel-Chrome-Molybdenum steel which is case hardened and core refined to give the ultimate combination of strength and hardness. Precision CNC Machined to extremely tight tolerances. Case hardened and core refined 655M13 Nickel-Chrome-Molybdenum alloy steel to give the ultimate combination of strength and hardness. Self-cleaning mud grooves between every tooth on both sides help prevent dirt build up. ULTRALIGHT REAR SPROCKET. Renthal Ultralight rear chainwheels are manufactured to extremely tight tolerances from a special material developed to withstand the rigors of Supercross, Motocross and Enduro. The 7075 T6 aluminum alloy rear chainwheels are 66% lighter than steel, yet incredibly durable. Their advanced tooth profile, concentricity and accuracy of fit provide maximum power transfer and long-life. Renthal's combination of a very high strength base material and an exceptionally hard wearing surface result in significantly increased chainwheel life