Specifications Material: 7005 Aluminium Alloy Components: Derailleurs Structure: Ceramic Bearings Color: Red, Blue, Silver (optional) Size: 11T, 13T (optional) Use: For 7/8/9/10 speed Diameter: 11T-40mm, 13T-50mm Package Weight: approx. 20g-11T, 23g-13T Fit For: For 4/5/6mm roller screw axis Note: Please allow 1-3mm error due to manual measurement. Thanks for your understanding. Monitors are not calibrated same, item color displayed in photos may be showing slightly different from the real object. Please in kind prevail. Package Included: 2 x Ceramic Bearings LIGHTWEIGHT AND DURABLE: Bike jockey wheel pulley is made of cnc aluminum alloy, which is lightweight and durable.FOR MOST OF THE REAR DERAILLEUR: Bike jockey wheel apply for most of the rear derailleur on the market, support 7/8/9/10 speed.GREAT PERFORMANCE: Rear derailleur pulley is anti-rust and corrosion resistant anodized. These pulleys run on smooth ball bearings.BIKE ACCESSORY: Rear derailleur pulley is a necessary accessory for your bicycle. It offers you a better cycling experience.