Genuine OEM Volkswagen flat head socket bolt, part number N91178601. This fastener is designed for flush-mount applications where a low-profile head is required to prevent interference. It is located in the cooling system assembly as shown in the diagram. The bolt features a precision-machined socket drive for secure installation. Genuine OEM fasteners are engineered to provide the exact thread pitch and head profile necessary for secure, vibration-resistant assembly in sensitive cooling components.