Anyone having issues with thread engagement on the outflow side of Watts LF7R check valve?

[Mr Blint]

I was trying to thread a 3/4 brass male NPT thread into the outflow side of a new Watts LF7R check valve, and tried several different ones, and also tried a 3/4 copper adapter, but couldn't get any of them to go very far in at all. Normally I have three threads remaining exposed but with Watts it was 6, or 5 if I really cranked on the wrench. All of the threads looked fine. I've read one other person having the same issue with the same model valve and they couldn't get it to stop leaking with teflon tape or pipe dope.