Renthal 520 Conversion Steel Front Sprocket BMW S1000R / S1000Rr / S1000Xr Renthal's Front Sprockets are a long lasting, hard wearing alternative to OEM replacements. Renthal CNC machines each sprocket from a specially developed case hardened and core refined 655M13 Nickel-Chrome-Molybdenum alloy steel. Features: Precision CNC machined to extremely tight tolerances for maximum performance Case hardened and core refined 655M13 Nickel-Chrome-Molybdenum alloy steel construction to give the ultimate combination of strength and hardness