You can stack these coasters with each other and they should self align, or you also can just stick it to your fridge, or anywhere that a magnet would stick on. This way your coasters won't get lost so easily

This sticky coaster is supposed to have a disc magnet of 10 x 1mm dimension inserted during the print paused sequence. So the disc magnet will be embedded into the coasters themselves. Please refer to the image for the best magnet arrangement

Just adjust the z-scale of this coaster if you have different magnet thickness, then cut top and bottom to make them thinner