使用它可以很方便地区分磁铁的极性。It can be used to easily distinguish the polarity of magnets.

需要用到直径5mm或6mm的圆形磁铁各三颗（也可以更多），安装时，把三颗磁铁按NS SN NS的顺序，这样磁铁之间的斥力会使磁铁稳稳的停留在打印件里（如下图），这样可以适合不同厚度的磁铁。Three circular magnets with a diameter of 5mm or 6mm each (or more) are required. When installing, the three magnets should be arranged in the order of NS SN NS. This way, the repulsion between the magnets will make them stay firmly in the printed part (as shown in the figure below), which can be suitable for magnets of different thicknesses.

附带一个区分磁铁磁极的方法：用细线或其他软的东西（我用一条纸巾）把磁铁吊起，当磁铁静止后，指向地球北极的一端为北极（N），另一端为南极（S），可以用手机指南针功能。Attached is a method to distinguish the magnetic poles of a magnet: use a thin line or other soft object (I use a tissue) to lift the magnet. When the magnet is stationary, the end pointing towards the North Pole of the Earth is the North Pole (N), and the other end is the South Pole (S). You can use the compass function on your phone.