Just print and press in the x4 magnets from McMaster CARR https://www.mcmaster.com/5862K108/ and then magnet right onto your OD caliper tips. Magnets hold the tips in place to allow for center to center or center to edge measurements.
I printed in petg so they fit a little snug which is fine since I don’t have the magnets. they are pretty accurate and was able to sand to a sharper point for better accuracy