Shimano ultegra 6800 bottom bracketthe shimano ultegra 6800 bottom bracket has been reduced in size and shaves 14g off of the 6700 version features hollowtech ii integrated bottom bracket uses a wider bearing placement and larger axle diameter for increased stiffness and efficiency hollowtech ii integrated bottom bracket seal design has minimal bearing interface ensuring smooth rolling and increased durability use the tlfc37 or tlfc25 spanner adaptor tool in conjunction with the tlfc36 standar