The Shimano SM-BBR60 bottom bracket features is designed to match the 6800 Ultegra group and features a 25 gram weight reduction over the 6700 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. The internal diameter and the width of the cups is the same so this bottom bracket will work with older Hollow Tech II road designs as well.
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. But the good news is Shimano includes an adapter that nicely works with all the standard outboard bottom bracket tools. Select BSC (also known as English) or Italian threading.