[Size] The thread size of 6an is 9/16-18 UNF, id of spring lock is 3/8 inch, please measure before perchase. [Seal] The 6an male to 3/8 female efi fitting has a 37 degree flare fitting taper assures a tight seal and ease of operation. [Application] Can work with engine fuel rail,transmission cooler,fuel pressure regulator,fuel line,return line,fuel sensor,etc.compatible with water,fuel,oil,e85. [Material] Made of aluminum alloy 6061-T6.Spring lock is made of plastic.