Inspired by the LTT magnetic cable management holders I designed these to go with 16 mm diameter x 5mm high screw in magnets.  These use M3 countersunk screws and 4 mm high heat set inserts.

Magnets: https://www.amazon.com/gp/product/B0CR6JRFZL
Inserts: https://www.amazon.com/gp/product/B0CLKCQ2SH