The Acera M3000 ES300 Octalink 73mm Bottom Bracket from Shimano is a splined bottom bracket for use with Shimano Octalink chainsets. It features a large oversized 22mm diameter hollow spindle that is made from cold forged chrome-moly pipe billet, which reduces weight and increases strength and rigidity. Thanks to the Octalink splined axle/crank arm interface you have a more rigid crank assembly compared to a square tapered spindle. The sealed cartridge bearing assembly runs on oversized ball bearings with maintenance-free, high efficiency rubber seals to keep dirt, mud and water out and keep you rolling for longer. Available in 73mm x 113mm, 118mm, 121mm or 126mm.