Wood corbels are braces. They are used to hold up shelves, fireplace mantles and countertops, if the top overhangs the cabinet more than 6 inches. They can be ornate or simple, and are characterised by a French curve on the front with a 90-degree angle on the back. The shelf or mantle sits on top, with the long end of the French curve pointing down. They are nailed or screwed on from the front and top. The do-it-yourselfer can install these by following a few steps.
Locate a stud in the wall with a stud finder.
Place the corbel against the wall on top of the stud under a shelf at a 90-degree edge against the wall with the French curve facing out. The corbel should be small enough so that when it's against the wall under the shelf, the shelf will overhang the end of the corbel by a minimum of 1/2 inch.
Drill a hole in the bottom of the corbel using a cordless drill and 3/16-inch bit. The hole should be 1 inch up from the bottom of the corbel. Drill lengthwise through the edge of the corbel aiming for the stud. Drill through the edge and allow the bit to drill into the wallboard 1/4 inch, if there is wallboard on the wall.
Insert a screw into the hole long enough to penetrate through the end of the corbel and sheetrock and into the stud. Screw in the corbel to the stud with the screw gun.
Drill three holes down through the top of the shelf, lining them up with the top of the corbel. Insert screws in the holes. Screw in the shelf to the corbel with the screw gun.
Use a decorative wood plug on the front of the corbel to cover the hole that you used to screw the corbel to the wall. If the corbel is 3/4 inch thick or less, pre-drill the corbel with a 5/32-inch bit before screwing it into the shelf from the top.
Always wear safety glasses when working with wood.