The casing placed around the ceramic magnetic round base focuses the strength of the magnets to the exposed surface thus providing a much higher holding strength than a same sized magnet without the steel cup. The magnetic circuit closes through the holding surface so the magnetic field leak is minimized. The steel cup provides a protection on the magnet which increases the lifespan of the ceramic round base magnet.
The magnetic round base is also known as cup magnet. Ceramic cup magnets are great for science projects, craft projects & are a ceramic ring magnet in an attractive protected casing with all of its magnetic energy focussed in one direction.