1Application: The chain tensioner roller is applicable for 49cc 66cc 80cc bike Engine Motorized Bicycle, please check before ordering. 2Function: Keep the chain can in an appropriate tension during the transmission process, so as to avoid chain slippage, jumping, tooth loss, etc. 3Fine Workmanship: Chain tensioner has smooth rotoring and longer life. Easy to install, protects swing arm and helps guide chain correctly. 4Material: Made of high strength metal alloy, it is not easy to deform, provides strong rotational force support, and ensures easier maintenance operations. 5Fine Workmanship: Professional manufactured, exquisite workmanship with unique design, ensure stable performance and high reliability.