Summary

We hang our Christmas stockings from a small beam under a shelf (approx 18mm wide) so I made a simple clip to fit over it.

Or, super-low-poly elephant, I'm not one to judge.

Unless you also have an 18mm beam, you'll probably want to adjust for your sizing, so here's the source:

https://www.tinkercad.com/things/aDkpBe9YkQD-stocking-hanger