Aluminum connector by TurboWorks. Purpose: oil system, water system, fuel system. For use with rubber and nylon hoses. External diameter 6mm. 3mm Suitable for AN4 5.5mm TurboWorks Aluminum adapter. Usable for: oil system, water system, fuel system. For use with rubber and nylon hoses. TurboWorks aluminum connector. Purpose: oil system, water system, fuel system. and nylon.