It's been too long- I'm not sure of the size. I've also seen someone use the end of a triangular file. And if you don't care about the screws (and the case, depending on how deep they are counter-sunk), you can use a dremel to cut slots in the screws to fit a regular flat-blade screwdriver. I've also seen a screw removal bit at the hardware store - you drill a hole in the screwhead and then insert the bit, which grabs hold of the screw. Or you are welcome to send it to me if you want.