Genuine OEM Volkswagen Socket Head Bolt, part number N91108501. This bolt is used to secure engine accessory components, such as the belt tensioner assembly, to the engine block. It provides a secure, high-torque attachment point for critical rotating accessories. Genuine OEM fasteners are essential for engine accessory mounts because they are engineered to handle the specific vibration loads and thermal expansion of the engine, ensuring that accessories remain properly aligned and securely fastened during operation.