U need a drill press and make sure the cylinder and then the head is flat on the drill press. Get an appropriate size drill bit to accommodate the m7 stud and drill both the cylinder and the head to that. I do this on hobbit builds but there isn't usually enough material on e 50 cases to do all four so I would stick to the single stud u stripped. My assumption is that u already drilled the case. If u did the case and u enlarged the stud hole without freehanding the overdrilling ( as in u retapped the m6 to m7 without first drilling it , then I assume the hole is at a perfect right angle to the case. Just to be certain put the stud in and make sure it is at 90 degrees to the top of the case. If u freedrilled it , then oh oh