Summary

These parts are for hanging things in 19" computer racks (and other places).
The rack hanger was specifically designed to fit in 3/8" square holes in various places on the rack. These can be printed in either a hard plastic like PLA or TPU.

These parts are meant to be used with a loop of string in a cow hitch knot.

The string hookend is designed to have a loop of string hitched over it, and then wrap the loop around a bundle of wire, and pass the hook end between the pair of strings that make the loop. For this to work, there must be enough tension on the string to keep it in the hook.

If the rack has two holes next to each other or a hole near an edge, the string loop can be hitched over the edge. If only a single square hole is near by, the rack hanger can be used. If the rack has a large slot connected to a square hole, the hanger with string attached can be passed through and then slid into the square hole and pulled through with the string. If the back of the hole is available, the hanger can be passed through from the back. If the back of the hole is not accessible, a TPU hanger (80% infill recommended) can be printed and squeezed into the hole from the front. (Note: I've had PLA hangers delaminate under heavy pressure, the TPU ones seem to be able to take a lot more.)

These can be hung from the top or sides of the rack, from the square holes in the rails, or the string could be looped around screws if there are convenient screw holes. Various rack manufacturers provide different holes in different places, so look carefully in the area you want to put your wires to see what is available.

These can be used to bundle cables together and restrain them, or to hang KVM cables temporarily, or anything else (headphones from a hard drive magnet).