Super Magnets are made of neodymium, the most powerful magnetic material in the world! The largest size shown here is only the size of two dimes, but strong enough to hold a 1/4″ thick pad of 3″ x 3″ sticky notes to a metal filing cabinet! Super Magnets are great for projects that require extreme strength in a small size. Due to their extreme strength, these magnets are NOT FOR CHILDREN, as they can pinch fingers. Each magnet is 3mm (.118″) thick and is available in three different diameters.