Due to Covid, children returning to school will be required to bring their backpacks into the classroom to avoid crowds at lockers. My wife, who is a teacher, asked me to build a hook so her kids can hang their backpacks at their desks, rather than pile them on the floor.

This hook was designed to be sturdy -- it can hold a backpack full of textbooks at the recommended print settings (wall-thickness of 1.2mm, with 20% infill, PLA or PETG).

Instructions:

Measure the target desk and find the stl that is closest to that (note, 3/4" desk will translate to 18mm).

Print on it's side -- no support required. Any material will work, but I used PLA. Print with at least 1.2mm walls (three 'loops') for most printers, with 0.2mm layer height, and 20% grid infill. At this setting most printers will print it in under an hour.

There are three methods to attach to a desk:

1. Friction fit -- if the desk is exactly the right thickness this will stick on quite well, and you may not need any fasteners. If it's a touch to loose, you can wrap electrical tape around the middle to tighten the gap. These might fall off when children are removing their bags, but they're easy enough to put back on.
2. Nut and bolt clamp: The hole in the center is designed to take a size 6-32 nut and bolt. Tightening the bolt will effectively clamp the hook in place. I'm concerned that the weight of a heavy bag might warp the model enough for it to come loose in this case. I would highly recommend using a wood screw over this method.
3. Wood screw: You can also fit a woodscrew (#6 x 1" or so) through the bottom hole, and screw it directly into the desk. The hole at the bottom of the desk will not be noticable, even when it's removed. Predrilling a pilot hole might make this easier if you're installing a lot of these.

I can also post other sizes if anyone needs them

Why this is important

As everyone knows, Corona-virus can be transmitted in tiny little droplets which float in the air. These droplets are heavier than air, and tend to fall to the ground within a meter or two of being exhaled. The problem is, that once on the ground, the virus doesn't magically disappear -- it just stays on the floor... A backpack placed on siad floor, and then picked up can allow the virus to spread from the floor back to a child's respiratory system. Hanging backpacks should reduce the risk of this type of spread.

Both children and teachers should be conscious of the fact that floors are one of the most likely contaminated surfaces in a building as far as corona-virus is concerned. Care should be taken to avoid touching the floors or things that have come in contact with the floor, and then touching one's face (and yes, that includes the bottom of your shoes).