I bought a storage cabinet with metal trays that pull out and was looking for a way to magnetize the miniatures I have for massive darkness, so when I pull the tray out they don't slide around everywhere.  I started with a very thin 1mm magnet but it just wasn't strong enough. I switched to a 9mmx3mm magnet it holds much more strongly now.   

This first STL file is sized to fit a common mob base.  I'll work on creating new bases for the roaming monsters and larger mini's.  

Everything press fit on without glue. These are the magnets i am using currently:  https://a.co/d/0Mz10Cz