Box Two Prime 9 X-Wide Rear Derailleur Fewer Gears, Same Performance If you're looking to increase the performance of your bike, upgrading your drivetrain is a great place to start. The Box Two Prime 9 X-Wide Rear Derailleur is designed to provide high-performance shifting with fewer gears to shift. It is optimized for 11-50T cassettes and offers durability and performance for the most demanding terrain. It features a forged inner and outer cage, closed bushing pulleys, durable 3D forged linkages, and a Pivot-Tech Cable Stay. Features Limited-slip clutch engages instantly with constant torque for less chain slap, better chain engagement, and no dropped chains Prime 9 technology offers the same range as a 12-speed drivetrain, with fewer gears to shift through Optimized for 11-50T cassettes | Box Components | Box Two Prime 9 X-Wide Rear Derailleur 9-Speed, Long Cage, Matte Onyx