I often put my reading glasses on and take them off again throughout the day.
In between uses I like to store them in a spectacle case.
After a while, the hinge-joint on the top usually gives in and it's time for a new case.
I solved this problem with 4 Q-10-10-05-N
They are powerful enough to make the spectacle case close again (provided that the case is reinforced with iron).
This way, you always have a few magnets handy when you need to hang up a poster for a presentation.