The magnetic poles of a ring magnetic disc can be magnetised in two ways; axially and diametrically. An axially magnetised ring magnetic disc is magnetised through the length of the magnet, whereas a diametrically magnetised ring magnetic disc is magnetised through the diameter.
Hole
The hole in the ring magnetic disc is created at the time of manufacture and has the same diameter through the entire depth of the magnet. This distinguishes it from the hole in a countersunk magnetic disc, which tapers from one magnetic face to the other, in the shape of a cone .
The hole in the ring magnetic disc is used to attach the magnetic disc to a large range of of objects such as a fishing line.
The ring magnetic disc is not technically used for fishing, it is however used to fish ferromagnetic items, such as a bicycle or coins, out of a river.
Keeper
The steel keeper on a ring magnetic disc must be removed before use to allow the magnet to work to its full potential. The keeper is a soft piece of iron temporarily added between the two ring magnetic discs, when multiple magnetic discs are stored together, to prevent them from demagnetising.
