The Articulated Cuttlefish model by TechnicaL has a perfect hole on the bottom for some inserts. My first idea was to make an insert where I could attach a magnet, but my kid thought it would be better to make a beak (how else would the cuttlefish eat).
So I whipped together both.
The intended magnet is 10x3 mm with a screw hole and I used 2.5x10 mm regular flat head screws.
The print setting for the magnet insert doesn't matter too much, but for the best quality for the beak you might consider printing that at 0.1 mm layer height.
The inserts are designed to be press fitted, so the tolerance is pretty tight.
Included there are also insert files for printing the cuttlefish model at 70% (which is the size of the print in the photos).
The author marked this model as their own original creation.