Holds through glass. Simply place a magnet on each side of the glass, then hang a sign, banner or decoration. Can be used with single pane windows or as single hooks on metal doors. If used on a metal surface, each hook will hold up to 35 lbs. Protective coating helps prevent scratching. Recommended use for single-pane windows only. More About Ceramic Magnets: Our hard ceramic ferrite magnets are composed of iron oxide and barium or strontium carbonate. Ceramic magnets exhibit relatively good holding strength for their price, making them a popular choice for many consumer, commercial and technical applications. Ceramic magnets have so many practical uses including; craft projects, refrigerator magnets, badge holders, latches, display boards, loudspeakers, security systems, motors, generators & alternators, lifting magnets, brakes, clamps, switches & relays, sweeper magnets, science projects, toys, games, motors, magnetic couplings, POP displays, advertising giveaways, promotional items, novelties & much more.