I had some unused space next to a set of shelves I build, so I designed and printed a hanger to snugly fit onto it and hold other things. The primary design goal was to hold my 3M Worktunes headphones, but it also works very well for belts and other things that gravity works on.
Printed in Orvil3D Radiant Black ABS+, at 0.2mm layer height on its side. Printing on the side means that use, the forces work on all layers uniformly instead of all being concentrated on one single layer.
I made an 18mm version and a 25mm version to fit my shelves and my desk, but I supplied the .f3d file so feel free to change that to any thickness you like. The model is also parametric, so jump into the table and change just about any major value for your own purposes.