I have bought a AK-74 style brake that has buggered threads in the middle.  Someone put a set screw on the brake and that ruined the threads.  My brother is a machinist and he can straighten the threads out, but I would like to be able to tell him what the threads are exactly so he won't have to guess and spend lots of time measuring the threads.  He has used a thread gauge already (both metric and standard), but they do not seem to fit.  Any help would be appreciated immensely.

Well, it seems that after doing some intensive research the threads are 1/2 - 28.  If I am incorrect, then please let me know, because my brother will be re-tapping this brake to fit this thread profile.

http://www.ar15.com/forums/topic.html?id=49967

I found the answer on the above thread...