Features: The ceramic inner bearing designed specifically for bicycles has minimal friction and significantly improves performance due to smoothers transmission. It can effectively suppress the horizontal swing of the chain and make speed changes more accurate. Provide low friction, achieve stable chain retentions, and achieve quick gear changes with minimal resistance. The smoothness is guaranteeds. Adopting ceramic bearings, it has a smoothers and faster response, and a snap-rings design, without worrying about the bearing rubbing and causing abnormal noise. Two reducers sleeves are provided as a gift, with strong compatibility. After installation, they can be converted into 4/5MM Peilin bearings, providing flexible-rotation. When purchasing, please check the specification number of teeth on the bike. In principle, it should not be greater than the number of teeth on the guide-wheel of bike, otherwise it may not be usable. Specifications: Material: Aluminum-alloy Color: Black/Red-color/Gold/Silver Model: 11T/12T/13T/14T 11T diameter: Approx. 41.6mm/1.64inch 12T diameter: Approx. 51mm/2.01inch 13T diameter: Approx. 54mm/2.12inch 14T diameter: Approx. 57mm/2.24inch Package Includes: 1x Jockey Wheel(with screws) 2x Reducing Sleeve note: Please allow 1-2cm errors due to manual measurement, make sure that you do not mind before you order. Due to the difference between different monitors, the picture may not reflect the actual color of the item.