Quote Originally Posted by J57ltr View Post
3/8" NPT is a little large the hole is just over 1/2" for the tap, 1/4" NPT would be a better choice and 3/8-1/4 NPT reducer bushings are easy to find even at Home Depot.

Jeff
that would explain why I smoothed down the bottom 3 threads of the tap. I found someone that might be able to tig weld the manifold, which will be a lot easier than tapping and threading. If the welding part doesn't work out, I have a friend that has more tools than I, that will help tap the holes and plug them.