Magnet keeper

[1] Keepers also have a useful safety function, as they stop external metal being attracted to the magnet.

[clarification needed] Many magnets do not need a keeper, such as supermagnets, as they have very high coercivities; only those with lower coercivities, meaning that they are more susceptible to stray fields, require keepers.

Each domain carries its own small magnetic field, which can point in any direction.

When all the domains are pointing in the same direction, the fields add up, yielding a strong magnet.

When these all point in random directions, they cancel each other, and the net magnetic field is zero.