Genuine OEM Volkswagen Collared Bolt, part number N91143901. This fastener features a collared head design, which provides a precise seating surface for mounting components within the engine cooling assembly. It is used to secure brackets and cooling system parts, ensuring they remain fixed under vibration and thermal expansion. Genuine OEM bolts are manufactured to exact tolerances to ensure proper clamping force and thread engagement, which is critical for preventing leaks and mechanical failure in cooling system components.