I wanted to use some tubes (d=10mm) I had left over to make a hanger for my tools inside the shelves, and so I came up. It fits perfectly in the shelf slot.
The shelves I have are these, I imagine they could also work with other shelves if the slots system is the same:
https://www.hornbach.de/shop/Schwerlast-Steckregal-Schulte-verzinkt-1800x900x450-mm-5-Boeden-Tragkraft-1400-kg/5800555/artikel.html
The author marked this model as their own original creation.