I legit went and bought a pack of Nutter Butter cookies to design this fidget. Not that I needed an excuse to get them, of course. ;-) I traced the design from a photograph I took of an actual cookie, so the dimensions are pretty much spot on.
You will need twelve (12) 8x1mm round magnets to install into the print at the pause point prior to the start of the layer at 1.3mm. You will also need some 4mm OD PTFE (ID doesn't matter, but 2.5 or 3mm ID is easier to snap in) as well as some 4mm steel bearing balls.
When the printer pauses, or when you manually pause it at the right height, install the magnets and make sure they fit snugly. If they are loose and you have a hot end with ferrous metals (such as a hardened steel nozzle), then you'll want to put a drop of super glue down as you install the magnets. Stock MK3 printers do not have anything the magnets will stick to. Don't forget to flip the polarity of your magnet stack when you move from one cookie to the other. The polarity in the filling piece (with the two small square openings) doesn't matter because it can just be flipped over.
Once the print is complete, install a piece of PTFE into each cookie in the long slot. It should be just shy of the full length of the slot (39mm). Plop a 4mm ball into the two square pockets of the filling piece and put it all together. If you did it right, it will work just like in this video…
The author marked this model as their own original creation.