Note - please go to the improved version of this backpack hook below:

Heavy Duty Backpack Hook V3 - Free 3D Print Model - MakerWorld

I carry a heavy backpack as I have an engineering laptop and the various hooks I found were inadequate.  Enter my over-engineered backpack hook.  I printed this using esun PLA+ for a super-clean print.  For strength, I printed the model at 40% infill with 5 walls and it is rather beefy and uses a good bit of filament for that level.  You could probably get away with a wall or two less and less infill if you are hanging a purse, lighter backpack, headphones, etc.

The “jaw” has a minimum surface thickness of 6MM (~¼") and a maximum of 47MM ( ~1 13/16") so will accommodate a thick desk surface.

The bolt face has a hole in the center that uses a pin to keep the pressure plate centered and able to spin.

Note that the bolt hole is 10MM which is about the largest opening that will successfully print without the overhang being too much to print cleanly.  I have printed this several times for office-mates and it has worked every time.  Always make sure your filament is dry and calibrated for your printer.