Our neodymium magnets with countersunk holes have two shapes, one is hole in round shape magnets, the other is hole in block shape magnets. A countersunk hole in a magnet provides a very convenient way to fix the magnet onto a surface securely by using a matching screw, such as M3, M4, M5, M6, M8, M10 and so on. Sometimes, the buyers do not know exactly that which polarity should they use for the final application. The simple way is if you use the magnet to attract to a steel surface, there is no difference. But if you plan to use these magnets to attract to each other, then the quantity will be north polarity in half, and south polarity in half. If you plan to use this magnet to attract to your own magnet, you need to choose the different pole to match them up.