Vice Jaw Pads, three sizes 3 inch, 4 inch, and 5.5 inch.

6mm magnets press fit (use the vice!) will accept 2.5mm or 3mm magnets.

Print in PLA (would also work in PETG and have a big more “give”).

Extra draft mode so it prints fast (we're not looking for pretty :-), 5 bottom shells to strengthen the side that faces the workpiece and 25% infill for crush strength.