The CeramicSpeed Oversized Pulley Wheel System provides optimization and increased efficiency of the rear derailleur through its extremely low-friction bearings and unique overall design. FEATURES: Features 13-tooth upper and 19-tooth lower, aluminum pulley wheels with Grade 3 Silicon Nitride balls Robust cage crafted from polyamide and carbon fiber for durability and light weight Hardened steel bearing races Only compatible with Dura Ace 9100/9150 and Ultegra 8000-SS/8050-SS Not compatible with Ultegra 8000-GS or 8050-GS (medium cage) nor with the clutch equipped Ultegra RD RX800/RX805 SPECS: Largest Cog: 32 Fits Brand: Shimano Fits Model: Ultegra R8000-SS , Ultegra R8050-SS/GS , Dura-Ace R9100 , Dura-Ace R9150 Drivetrain Speeds: 11 Defined Color: Red