Everyone says in his comment and I confirm it again! It was beautiful to say they will be small and even very small, surprise is inversely proportional to the size of the magnet translation for those who do not follow: very small magnets, huge surprise! ;-) To give an idea, you say a letter key on your keyboard, you can put about 25 !!! (Of course, a single layer!)
At this last detail, they fulfill their role. They are powerful enough to hold an A4 sheet (with 2 magnets, that is enough. It's safer with 4)
