Pairs of beveled strips that interlock to support shelves, cabinets or pictures are called French cleats. They’re great for hanging any shelf or cabinet and have a few advantages in certain situations.
First, the cleats work well for heavy cabinets because you can easily mount the wall cleat and then simply lift the cabinet and “hook” it on. There’s no need to support a heavy cabinet temporarily while you drive screws to anchor it.
Another common use for French cleats is to create a flexible system of shelves or cabinets. You can screw one or more lengths of wall cleats across the entire wall, and then easily relocate shelves, or add more shelves at a later date. Make cleats by ripping strips of 3/4-in. plywood with a 45-degree bevel on one edge. Screw one strip to the wall and the other to the back of the shelf or cabinet.
These nifty little fasteners are actually designed to attach table and desktops to aprons (the vertical skirt around the perimeter), but they’re also a handy solution for hanging shelves. You can buy a pack of eight at woodworking stores or online.
The only caveat is that the top of the figure-eight shows above the surface of the shelf, so it may be visible if you hang the shelf low. Try to position the figure-eights where there are studs, if possible. You can use good-quality hollow-wall anchors if the studs don’t line up with the figure-eights.
Drill a recess for the figure-eight. Use a spade bit or Forstner bit to drill a slight recess in the back of the shelf to accommodate the thickness of the figure-eight. Then chisel out the remaining wood until the figure-eight sits flush to the shelf. Attach the figure-eight with a screw.
Attach to the wall. Mount the shelf by driving screws through the figure-eights either into hollow-wall anchors or into studs.