Features: It is used to prevents drop when folding the chain hook of bicycles. It is installed on the rear derailleur guide wheel frame. Designs specifically for folding bikes, this tensioner ensures a perfectly fit and function. Make from aluminum Alloys, this tensioner ensures durability and light weight performances. Easily adjustable speed setting for perfectly chain tension, enhancing your cycling efficiency. Features a rear derailleur mount and guide wheel for stable, none drop chain management. Specifications: Materials: Aluminum Alloys Color: Red Color/Black Color/Gold/Silver Size: about 8.1x2.6cm/3.19x1.02inch Package Includes: 1Pc Chain Tensioner note: Please allow 1-2cm errors due to manual measurement, make surely that you not mind before order. Due to difference between different monitors, the picture may not reflect the actual color.