Shimano Alfine SG-S7001-11 Sun Gear 4 Description: The Shimano Alfine SG-S7001-11 Sun Gear 4 is one of the components within the internal assembly that helps to change the gears inside of an Alfine 11-speed internally geared rear hub. Its purpose is to drive the planetary gears when performing a gear shift, and the result is a different gear ratio will become engaged within the internally geared hub. This is a factory replacement part to help to replace worn or damaged parts to restore optimal shifting performance of the internally geared rear hub. Features: Includes only the hardened steel sun gear 4 Hub axle unit, carrier units, bearings, and other components of the internal assembly sold separately