This simple hook uses gravity and balance to hang items like headphones, cables, light strings, whatever you want from IKEA BROR metal shelving unit brackets. 

Print in PETG or PLA or ABS, no resizing required. Higher infill for heavier objects. You can scale it on the z axis in the slicer to make it as wide or as thin as you need.

See photos for installation instructions. You can put a piece of double sided tape to stop the hook from camming out, or install without tape for easy tool-less repositioning!