The Brace attachments (minimal or isogrid reinforced) slide into the shelf platform. The middle of which are 8" center so that you get 16" on center for screwing into studs. There are also slots ½ inch and 1 inch on each side (the intent to maybe have an attachment for drawers or something else, but also helps on corners where the studs aren't 16" on center).

This has overlapping top and bottom pieces for the platform which interlock together so you can get a platform that can be longer than your print bed and stiff enough for the shelf.