Genuine OEM Audi Auxiliary Belt Tensioner, part number 059903133J. This essential component is responsible for maintaining the correct tension on the engine's auxiliary belt, which drives accessories like the alternator, power steering pump, and air conditioning compressor. It is mounted on the engine block, providing consistent belt tension to prevent slippage or excessive wear. Constructed with a robust metal body and a durable pulley, it weighs approximately 0.745 kg. Opting for a genuine OEM tensioner ensures precise spring calibration, high-quality bearing performance, and exact fitment, which are critical for preventing premature belt wear and accessory malfunction.