The Shimano SM-AD91 Clamp Band Unit is designed for frames without braze-on hangers and is compatible with both Di2 and mechanical derailleurs. Featuring a built-in aluminum plate, it stabilizes the derailleur during gear changes, protecting your bike frame from potential damage. Available in 31.8mm and 28.6mm sizes, this clamp ensures secure and reliable shifting performance. Essential for maintaining drivetrain integrity and extending the life of your bicycle components.