This is a plain board for mounting 20x20 boards on 30x30 stacks.
Outer 30x30 holes are wide enough to pass screw thorugh.
Inner 20x20 holes are tighter so they might hold the screw without need of nut. (TEST THIS!)
If you dont use nuts to hold 20x20 board, you are doing it know this and take full responsibility for any damage done.