After a week of printer calibration I ended up with quite a few of the Voron test cubes (https://github.com/VoronDesign/Voron-2/blob/Voron2.4/STLs/TEST_PRINTS/Voron_Design_Cube_v7.stl) and didn't want to just throw them away...

This is a small insert that will allow you to fit a 7mm diameter 3mm tall round magnet into the Voron test cube, and then you can use it as a fridge magnet. Just needs a bit of superglue.