Just a basic S hook with a 90 degree twist. I made these to hang a fan from hooks above my bedroom door. I printed a pair of them in about 40 minutes on a really slow printer.

In printing these consider what you're going to be hanging with them. For relatively heavy objects, such as the above mentioned fans, I recommend 5 shells, 50% infill, and the thickest layers you can do. For lighter objects you can probably get away with less shells and/or infill, but thick layers are probably still a good idea. These things are meant to be functional after all, not pretty. In any case you will need to enable supports.