I have a rebuild job on a Trooper MArkIII. Someone ham fisted the elevation screw on the rear sight, breaking the screw and stripping the threads in the frame. I have located a replacement screw, but need to determine the tap size needed for the threads in the frame. I will drill and tap the frame for a plug, then drill and tap that for the screw. Anyone know what the thread size is or where to find it? I have tried to match it to standard gunsmith taps but the thread seems to be somewhere near 6-60. Any help will be greatly rewarded ( or at least greatly appreciated).