These hooks take three 18mm x 5mm magnets.

One of the designs has a lip at the top. This allows you to have the hook at the top of the item (in our case a fridge) and the magnetic hook not slip down if the item being added is too heavy.

The other hook is just a normal hook.

I printed them in Creality PLA-CF, as that was what was in my printer at the time, but they should be able to be printed in anything