Version 2 of my basic S-hook. Made clip tighter, but springier.

Printed on PET-G, not tested on PLA, might work as well

There's versions with different gap size, all of them should snap easily on bar atleast 2-3 times the size of the gap. (3mm snaps easily on 7-8mm) 

Set perimeter count high enough, so there's no infill of solid layers. (4 perimeters is good for 0.4n)

You can make it handle more waight by scaling it thicker (on Z-axis). This might make it stiffer when inserting too. Test weight handling before hanging anything valuable or fragile

When printing multiple hooks, print one at a time (Advanced settings: Print settings > Output > Complete individual objects) for less stringing and better durability.