I needed a way to mount an esp32-cam case to a metallic surface and had some 20x4mm magnets laying around. I printed this in TPU and it turned out ok.

To make it work: Pause the print and insert magnets at the layer just before recesses for magnets will be bridged.

Ball diameter is 16mm so the mount is compatible with https://www.printables.com/model/960367-esp32-cam-plumbus-adapter and https://www.printables.com/model/742987-rpi-camera-holder-plumbus (probably)