I needed something to hang my rolls of wires, and have a nice rack shelf next to me, with lots of spare holes, so I decided to print these to slide into the slots.

The first one I printed (the one pictured) was a little too wide on the gap, causing it to hang a little, but I've since made it 0.2mm thinner, and added a version that has a "lip" on it, to keep things from sliding off.

ABS @ 230C, 120C build plate, 0.3 layer height, with support (for the top)