G&P receiver threading issue

[LUTNIT]

Okay, so I'm trying to swap front ends on a G&P SPR but ran into a really strange problem with threading. I'll list whats up:

-original G&P front end was put on a PTW, threading fit, also fits on TM
-cheap crappy Dragon Fire front ends fits on this G&P and a TM I have
-cheap crappy Dragon Fire front end does NOT fit on a PTW
-DBoys SPR front end fits on a TM but NOT the G&P

So G&P barrel nut fits on G&P, PTW (real steel), and TM.
Barrel nut that fits on G&P and TM will not fit on PTW.
Barrel nut that fits onto TM will not fit onto G&P.

All three of these statements seem to contradict each other. Does G&P somehow have dual threading or something? I thought maybe it was just really stiff so I put some more force on it with a barrel wrench and it stripped the first threading inside the DBoys barrel nut. I tried forcing the Dragon Fire barrel nut on a PTW with a wrench as well but it kept going on skewed, if I forced it straight it started to eat threading.

Any ideas or experience? Do King Arms or Madbull barrel nuts fit on G&P bodies?

[mcguyver]

The Imperial and metric thread pitch is really close. Close enough to be easily reworked, but enough apart to cause problems. Now, add in different surface finishes, materials and tolerances, and mixing and matching is going to be a problem. Easiest way to guarantee everything fits in every configuration is to have metric and Imperial thread files on-hand. They cost about $15 each.

But stick to quality parts, avoid the clone garbage and lessen your chances of being caught up in tolerance issues.

[LUTNIT]

Thus why the cheap ass crap doesn't fit on random other brands but G&P stuff fits on everything. The world is now clearer...except for ICS (lol but whatever, thats for another thread.)

Thanks