Dave Fawthrop wrote:

Modern magnets are wonderful. I have some 1cm dia which are N in the
middle S round the outside (or vica verca) and nothing on the back.

Modern neodymium-iron-boron (NdFeB) magnets are incredible. I have some of
these 'rare earth magnets'
http://www.axminster.co.uk/name/rare...nets-19790.htm

The ones the size of an aspirin are near impossible to pull apart. In fact,
if you aren't careful they catch your fingers.

Dave