Boyd tank fitting help.

[Mack B]

So I’ve had this tank since 2013 and just got around to installing it yesterday....I was building suspense.

Tank is gorgeous, problem I’ve ran into is everything I can find on the web says the feed and return is 3/8 NPT (non efi tank) but I can only get 2 threads of engagement on any fitting I’ve tried one either port. Except a random 16x1.5mm fitting I just happen to have. It fit like I expected the pipe thread fittings.

I’ve reached out to Boyd’s but I’m sure they are going to confirm it is pipe thread I’m dealing with, but in the mean time what do? I’m not comfortable leaving it like it is even if it doesn’t leak now. The lower bung appears to be a coupling welded in place, my thoughts is to try to run a 3/8 npt tap deeper into it. Anything else I could try before taking it to a fab shop to get an -an bung welded in? First 2 pics are the feed, last 2 is return on top