The Shimano Deore Octalink Bottom Bracket is a splined bottom bracket for use with Shimano Octalink chainsets. Features an oversize 22 mm diameter hollow pipe billet spindle which reduces weight while increasing strength & rigidity. The Octalink splined axle/crank arm interface results in more rigid crank assembly compared to square tapered spindle. ES51 has anti-corrosion treatment inside hollow spindle which when paired with a sealed cartridge assembly creates a maintenance-free sealed cartridge keeping out dirt mud & water. Cartridge design allows easy installation without adjustment.