Based on Supermagnete 15 mm donut magnet
http://www.supermagnete.fr/eng/R-15-06-06-N

The use of magnetic bearings (steel ball over a donut magnet or vice versa) allows 3 key advantages:
– Strictly no play
– Rapid assembly disassembly & therefore part exchange
– Dismantles in case of clash or out of range movement preventing damages to the machine & particularely the print head

These could be fitted with contact wires to check if there is a loss of a link & inform the control unit to stop or hold the print job

The chosen magnet are just sufficient for the StrongPrint head therefore if you intend to use a heavier print head you should choose to take slightly more powerfull magnets.