These magnetic clips use on whiteboards, file cabinets, or any magnetic surface. Great for holding folders, student portfolios, or large stacks of homework. Super strong magnet clips hold 20 pounds and up to 50 pages each. If they are pasted on magnetic objects, they will be strong and will not fall off easily. It can be directly adsorbed on any metal or magnetic surface but it is not suitable for glass, plastic, cement and other items without magnetic surfaces.