For some more info on pressing boards see
Step 1: Cut out the pieces
The holes at the head end of the screw are drilled a touch oversize so the screws can pull the boards nice and snug rather than binding in both boards.
I uploaded a .pdf with the pattern I made and used and you can tweak it of just make your own. It doesn't require a lot of precision, but I wanted it so that with my 3/4" thick board the whole thing still ended up being as the same size on all 4 small sides, and so that the three prongs at one end would line up so it can stand on end. Maybe you want something slightly different?
I used boards that were just under 6" wide so I scaled my drawing to make good use of the material. You could probably go an inch smaller or as much larger as you want and it would still work.