The Mark2 upgrade for an Ultimaker adds a second head. I wanted a place to hang the second head when I'm using the printer with a single nozzle, so I took the Mark2 docking plate and made it into a secondary mount to hang the second print head off the side of the printer when not in use.
This needs 3 more magnets, but it's the sames 6mm x 3mm ones from the Mark2 project.
Push the magnets into part B then superglue part A into the notch on part B.
https://www.magnetic-tool-changer.com/ for Mark2 project.