Here is a video that shows how much pressure I put on the top tube tank. And when pressurizing motorcycle tanks checking for leaks they only pressurize to 8 to 14 PSI. In this video I go to 36 PSI if the tapping was not done well enough that filler neck would come shooting out of that tank. I think you can say with out a doubt the threads have taken quite nicely don't you?
YouTube - Felt Twin Test for Leaks Top Tube Tank Part 3