Nicholas is right when he says not all routers are the same. When I got my first router (old craftsman) it mounted to the small craftsman table using the same screw holes as the mounting plate (no other way to do it). When I got my Hitachi M12V, I secured it to a sheet of 3/8" plywood, using the plate mounting holes (after removing the plate of course). I just needed to get longer screws. Mine are 5mm diameter and I found them at Ace hardware. I then put that sheet of plywood onto my B&D workmate and used it that way till I built my router table using the OP table top. Then I switched to the 11" removeable mounting plates. If your router has larger threaded holes, they may be for various attachments that Skil has. Check it out.
If you never made a mistake, you never tried anything