Using the xtera box on my 66. I ordered some fittings to convert to an-6. I got the 16x1.5 and 18x1.5 Inverted. The 16-1.5 goes in not to snug till I hit bottom. was wondering if maybe I have the wrong fitting. i have herd I think on one of somebody’s posts that it was a 3/8” inverted. The box...