Genuine OEM Audi Engine Timing Chain Sprocket, part number 057109085A. This precision-machined sprocket is an integral part of the engine's timing chain system. It engages directly with the timing chain to accurately synchronize the rotation of the crankshaft and camshafts, which is vital for precise valve timing and engine operation. Made from hardened steel, it is designed for high durability. Using a genuine OEM sprocket ensures exact tooth profiles and material specifications, which are crucial for maintaining engine timing accuracy and preventing catastrophic engine damage.