I needed hook to hang bags or tools to my aluminum ladders. Ladder tube is rectangle profile roughly 19x40mm.
Hook is made to simply snap on the side of ladder tube. It is not meant to hold substantial height but it can do well for what I need it.
There are two models, one solid and one using less material. Solid one can hold larger weight.
Download models
https://www.printables.com/model/460131-aluminum-ladder-hook