These shelf brackets mount on the previously existing curtain rod screws in my bedroom. Your screws will need to have a thread diameter of <0.2" and a head diameter of <0.35". There are also holes on the bottom if you want to screw the shelf to the bracket, which I needed as I hung a plant off the side of the shelf. Speaking of the shelf, it needs to be ~7.25" wide and ~0.75" tall; I think I used this from Home Depot.

Make sure to use enough brackets and screw into a stud, I claim no liability if you stack a bunch of textbooks on your shelf and mess up your drywall :D

Print instructions

I would recommend printing flat on the build plate with >2 perimeters and >4 top/bottom layers so they screws don't rip out. Infill doesn't make much of a difference past 30% or so.