Hello: The set screws are metric. Try a metric 3mm size hex wrench first. If that does not work try a standard hex and see if that grabs them. Lastly you may have to drill them out or easy out. I have used the SPS metal hardware and they work great. Thanks, Eric
The head of the hex head screw is not stripped, it seems that the screw has stripped in the plastic, and will neither screw in nor out. It has stuck through into the memory system and is now preventing the removal of the comb.
Its been a while since I've adjusted mine. A friend of mine didn't understand how the beretta comb works. The holes in the stock are just access holes for the hex key. The screws won't back out through the holes in the stock. My friend didn't realize this and he turned out the screws - right up to the point that it split the entire side of the stock out. The center screw just locks a memory block in place, tighten that one so the memory block isn't hanging up on the stock or the plate. Screw the outer screws in, then back them out a turn at a time. Keep checking to see if you can lift the comb out.
If you go more than a few turns and start to feel resistance, stop! You're backing the hex of the screw into the wood and you could split the stock.