I have a Paughco horseshoe oil bag and the fittings it comes with to run my lines are NPT. Are they usually very tight? I try to hand thread it but it so tight that it feels like I'm going to cross thread it. I wasn't sure if it's the chrome or if NPT is meant to be this tight. I've held off on using a socket or wrench because I don't want to damage the threads.

 

Try a non chrome fitting of the same thread. ( pipe fitting) See if it spins in.

 

Is there chrome on the threads? That doesn't help. Maybe run a die over them, they won't be seen anyway.

 

looked like there was chrome & gunk on the bung thread. I ran a tap in to clean them out but even that was tough to spin.

 

NPT or pipe threads are tapered threads. They typically get tight after a few turns. They're this way to make a tight, leak proof seal. They tighten up much differently than typical straight threads if that is what you're more familiar with.

 

I agree with jake24lt.
When machined there has to be an allowance for the chrome build up.

 

What size tap did you use? Got a matching die? Run the fitting on the die.