Fridge Bolt

A fridge magnet model of a 24mm nut threaded onto a bolt. Note that the model is one piece, the nut does not move on the bolt. Sized for three 8 x 3mm magnets (which you probably have left over from making motor visualizers). Magnets are completely inclosed. Even with the magnets enclosed it's good and strong. It has no trouble holding up thick or slick paper.

Printing

Any material, no need for supports or brims. I used 0.15mm layer height and a 0.4mm nozzle. If you slice it yourself, be sure to include a pause to insert your magnets before the pockets get printed over at Z = 3.8mm. The attached 3MF include slicing settings if you open it as a project in PrusaSlicer.