Made a simple ceiling hook for hanging stuff.

Attach with two M4 screws

counterbore: 2mm deep - 8mm wide

Print on it's side for maximum strength.
It's really strong! I think it can handle 40kg easy.
Not sure about the long term stress on materials like PLA. For my use it's plenty strong.

This S hook is a great pairing. I printed it at 60% scale.
https://www.thingiverse.com/thing:850300