I designed this simple Duck Model in OpenSCAD - code attached so you can make different sizes or remix.
The clutch recess for the magnet still wants a drop of superglue, but it's a snug fit, designed it so that you can always fit the magnet in by cutting 50% of the circumference out to make it clutch.
Feel free to take remix - make it arty or whatever.
Printing on Kobra 3 - with ACE Pro multi filament.
If you want to make different sizes you need to run the OpenSCAD code and change the top 4 size parameters and maybe the eye size, don't change the magnet size unless using different magnets. (Magnet diameter set to 8.1 for 8mm magnet, so assume 6.1 for 6mm magnet). Obviously scaling in a slicer would change the size of the magnet recess which would be annoying.
The author marked this model as their own original creation.