Neodymium magnets are one of the more common neodymium magnets. A Countersunk Neodymium Magnet, also known as a Round... more Neodymium magnets are one of the more common neodymium magnets. A Countersunk Neodymium Magnet, also known as a Round Cup, Cup or RB Magnet, is a powerful mounting magnet that mounts on a steel cup with 90 countersunk holes in the work surface to accommodate standard single-head screw neodymium magnets.