There is a hole in the middle of the weight plate, and there is a metal rod in the hole, and there are many holes in the rod. These holes are arranged neatly and aligned with the corresponding weights. This stick is connected to the lever with a rope. If you pull the lever hard, it will move with this metal bar. Because the metal rod is inserted into the weight, when you insert the pin into the weight, you will also insert the pin into the hole of the rod. The pin will drag the weight up with the rod, but the weight below will not move with it.