Shimano RD-R8150 Ultegra Di2 Rear Derailleur Bracket Axle Unit Description: The Shimano RD-R8150 Ultegra Di2 Rear Derailleur Bracket Axle Unit is a factory replacement part that connects select Shimano road and gravel bike rear derailleurs to a bicycle's derailleur hanger. If the stock bracket axle kit has become damaged, this replacement part will help to properly align the body of the rear derailleur for optimal shifting performance. Features: Includes the bracket, the bolt that goes into the derailleur hanger, and the B-Axle bolt that attaches the bracket to the rear derailleur body Specifications: Rear Derailleur Compatibility: Shimano RD-R8150 Ultegra Di2 | Shimano RD-RX825 GRX Di2