Adhere works to metallic surfaces with our Magnart Black Pin Magnets. Our pin magnets are made with a Rare Earth Neodymium magnet inserted into their plastic substrate. These whiteboard come in a pack of 12 black pin magnets. They are very strong for their size and can hold approximately 10 sheets of A4 pieces of paper to a magnetic whiteboard or any metallic surface. They have a diameter of 12mm and a height of 22mm.