The main wheel plate of a laboratory planetary ball mill is generally equipped with four jar holders, which can be used to hold the ball mill jars. The main wheel plate will drive the ball mill jars to rotate, and the jar holders themselves will also drive the ball mill jars to rotate in the opposite direction. The grinding balls in the ball mill jar impact, rub and squeeze the sample to achieve the effect of crushing and grinding.

When the planetary ball mill is running, the ball mill jar is in a state of high-speed rotation, which requires the balance on the main wheel to be balanced, otherwise it cannot rotate smoothly. According to this principle, we can put four ball mill jars on the planetary ball mill (i.e., one jar holder for one jar), or we can put two ball mill jars symmetrically, or we can put eight ball mill jars (i.e., two ball mill jars are placed one above the other on a jar holder).

If the amount of sample that needs to be ground is not large and can only be put in one ball mill jar, we need to place an empty ball mill jar in its symmetrical position to maintain the balance of the wheel under high-speed rotation.