Aluminum nipple by TurboWorks. Purpose: oil system, water system, fuel system. For use with rubber and nylon hoses. External diameter 19mm. 17mm Suitable for AN12 18mm TurboWorks Aluminum nipple hose.Usable for: oil system, water system, fuel system.For use with rubber and nylon hoses.Aluminum nipple by TurboWorks. Purpose: oil system, water system, fuel system. nylon.