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 axlecrank arm interface you have a more rigid crank assembly compared to a square tapered spindle the sealed cartridge bearing assembly runs on oversized ball bea