The Shimano XTR SM-BB93B bottom bracket features a 25 gram weight reduction over the M980 plus a new black-anodized finish. To achieve this considerable weight loss the external cup size is noticeably smaller thanks to smaller bearings and a reduced external diameter.

Other than the smaller cup and bearing size, the system is still Shimano's well proven Hollow Tech II design with a 24mm internal diameter and the benefits of a wider bearing platform, easy installation and serviceability. Improvements don't stop at weight reduction. New bearings and seals allow a claimed 50% reduction in friction so your cranks will spin more freely plus there is no pressing need to jump to ceramics.

As side note - your standard outboard bottom bracket tool won't fit directly due to the smaller external diameter.