If you're referring to the delta ring at the base of the upper receiver, then you may want to purchase a new one. Owning a G&G myself as a loaner, I found that the stock G&G delta ring is sized just a bit smaller than standard rings. With the stock ring I was unable to properly mount a Magpul MOE hand guard.
Purchasing a
King Arms Delta Ring from Jugglez at AirsoftParts.ca resolved my issue. I expect it would do the same for you. Make sure it's the KA version and not the G&P as the threading may be different. Not sure if the G&P ring is threaded for standard TM or it's own receivers (which are different).