Hy 51 2 Ton, what I think I am looking at in your picture is an inverted flare elbow, probably 3/16" tube, but it might be 1/4" tube. I am not sure that they make a "plug" for that fitting, but if you go to your parts store and buy a 3/16" inverted flare nut and a 1/4" inverted flare nut I think one if them should thread into your elbow. I'll look in my books and see if I can find a "plug" in either of those sizes. Okay, the Weatherhead part number for the inverted flare plugs are, 3/16" 131X3, 1/4" 131X4, hope that helps.
