Removed the two screw holes in the original model and replaced them with 3 embedded 10x3mm magnets.

Strong enough to hold normal metallic calipers.

I mostly did this to practice embedding magnets in prints. The magnet holes are marginally wider than needed (wanted to play it safe), therefore it rattles slightly but works great.

I manually painted supports - see image. Automatic supports would create supports in the magnet holes. I added a pause in Orca to manually place the magnets.