Designed for use with 9100 and 9150 Dura Ace drivetrains, the Shimano Dura Ace BB-R9100 Bottom Bracket features an advanced seal construction for a smoother rotation. Its small bearings are also lightweight. The Shimano Dura Ace BB-R9100 bottom bracket features smaller lightweight bearings and an advanced seal construction for smoother rotation and increased durability. It is designed to work in combination with the Dura-Ace R9100 crankset to offer optimal stiffness and a smoother pedal stroke.