umm, if you're refering to the fitting that attaches the hard line to the flexible hose, it's actually the right thread size for a 1/4 inch line, but has a 3/16 line going through it. i'm pretty sure they did that to avoid confusion on the assembly line. auto parts stores sell an adapter to go from a 3/16 line fitting to a 1/4 line fitting. inverted flare.