Genuine OEM Volkswagen Belt Tensioner Damper, part number 05E903305G. This part regulates the tension of the accessory drive belt, preventing slippage and ensuring efficient operation of components like the alternator. It is mounted to the engine and works in conjunction with the accessory belt system. Proper belt tension is crucial for the longevity of the belt and the components it drives. Genuine OEM tensioners provide the correct spring tension and durability.