What sz screws do the mntng holes in the bottom of the pedal basetake?

What size screws do the mounting holes in the bottom of the pedal base take? There are two Threaded Screw holes in the bottom plate under the pedals that are clearly intended for mounting a more secure base, but there is no indication as to what size screws these holes take. It's unfortunate that there's only two, but at least there's two, and not zero, and I would like to use them.