Feature:1. Supporting for various speed shifting. Offers you a better cycling experience.2. Can be applied for most mountain bike, bicycles, road bikes, folding bikes, etc.3. Adopting aluminum alloy and ceramic material, this product is very durable to use.4. This ceramic rear dial guide wheel is strong and light. Ceramic bearings ensure durability.5. Easy to install, there are 2pcs installation accessories which help you install easily.Specification:Item Type: Rear Guide RollerMaterial: Aluminum Alloy + CeramicColor: As shown in the pictureSpecification: 15TLength Size: Approx.55mm / 2.17inInstallation Size: Approx.6mm / 0.24in axesSmall Size: Approx.4mm / 0.16inLarge Size: Approx.5mm / 0.20in Package List:1 x Rear Guide Roller2 x AccessoriesNote:1. Please allow 1‑2mm error due to manual measurement. Thanks for your understanding.2. Monitors are not calibrated same, item color displayed in photos may be showing slightly different from the real object. Please take the real one as standard.