This is a mounting bracket to hold a piece of sheet plastic to a metal surface (e.g. a refrigerator) for use as a whiteboard. I’m using a piece of sheet acrylic I had formally been using as a cutting surface when cleaning up prints. I spray painted the backside white but I’m not convinced that helps when attached to a white fridge. If you do so, do not use more than one coat as many spray paints will peel off acrylic when the second coat is applied.

The openscad file should be parametric enough to easily change for whatever size magnets or plastic thickness you have available. I used 6mm x 1.5mm disc magnets (dia x thickness) and plastic about 2.3mm thick. The number of sockets is overkill for the strength of magnets I’m using. The magnets are all press fit in and no adhesive was used anywhere.

Support structures are included in the stl which make it suitable for printing in this orientation on my printer. They all pop off easily with a set of pliers.