This bracket is based on a standard shelf. Home Depot and Lowes sells Rubbermade brand shelves that I based this on. The bracket fits snug.G-code created by Cura.

The "nub" is on the side where you drill (use a hole punch first) a small hole to then screw in (supplied by the Ikea lightbar packaging). You'll have to cut off a few mm of the tip of the screw after first screwing in the screw, making sure you don't penetrate the the other side.