[Tx Firefighter]

That's normal.

The threads are 1/2 N.P.T. which is "national pipe thread"

They are not straight threads like a normal bolt has. They are tapered. The further you tighten, the tighter it gets. Be careful though, only tighten enough and stop. Too much can, and will, crack the manifold or fitting.

Use a sealant on pipe threads too. I use teflon paste. It will make the seal better without having to tighten it so damn tight and risk damaging something.