The Shimano Deore XT BB-MT801 Bottom Bracket is designed for Shimano's Hollowtech II two piece mountain bike cranksets. The MT801 bottom bracket benefits from technology already in place on the flagship XTR edition, and the trickle down means this bottom bracket is lighter and has less bearing drag than the previous XT model. Not only that, there's improved durability via updated seals to ensure mud and grime are kept out.