Hi, Gabe,
The actual plans that you linked to show that you drill and countersink holes NOT in the 'L' bracket but, in the sides of the back of the shelf.
After you screw that to the wall, you plug the holes with wooden plugs to hide the screw holes.
If you so desired, you could actually use a key-hole bit and make two key-holes in the 'L' bracket that would slip over screws in the wall but,
that would not be as safe a support as the screws in the holes provided in the plans.
God Bless! Spirithorse
