Installing Memory in new Imac

Has any one else had a problem with the screw that covers the memory chips? I could not find any screwdriver that fit it. Took a trip to the hardware store and bought some new screwdrivers that looked to be the correct size. Neither the phillips size 0 or size 1 fit correctly. I was really afraid to strip it! I finally used a small flat blade and it came right out. What size is it?