G&P metal body D Ring trouble

[GGTIMMY]

Ok, I bought a brand new G&P M16 A3 metal body and Fitted all the parts together, however, when i try to put on two different D rings on the body they will not screw on and need allot of force, I've tried to sand the metal body threads down a little but still no luck?

Do i need to buy a special G&P delta ring or what should i do? Any help much appreciated.

Thanks