The screws that hold the bowls on are all the same size, the DRAIN screws are different. i've seen 3 different types, one for a slot head screwdriver (very early models) one that uses a larger hex,(early 90's) I'm guessing around 4.5 - 5mm,, and the later ones that use the 3mm hex.
On BIG caution I want to throw out there is DON'T OVERTIGHTEN the drain screws? they're tapered and can literally "drive apart" the bowl and destroy it with a big crack! steve