Description: Made of aluminum alloy material, anti-rust and anti-corrosion, lightweight and durable. High rigidity ceramic bearing, super smooth and noiseless. Fits for almost all mountain bike of 11T and 13T, suitable for use 4/5/6 mm guide wheel screws. Easy installation. Necessary accessories for your bicycle. This bike guide roller pulley can reduce drag and improve cycle efficiency, offers you a better cycling experience. Specification: Material: Aluminum Alloy Diameter: Approx. 11T: 41mm/1.61inch 13T: 49mm/1.93inch Package Includes: 1 Piece Bike Jockey Wheel (with 2x Installation Hole Adapter Tubes Sleeve) Note: Due to the differences between different monitors, the picture may not reflect the actual color. There is 2-3% difference according to manual measurement, please check the size carefully before you buy the item. Thanks!