Chain block is a kind of manual lifting equipment. Its lifting principle is to pull the hand zipper by hand, and through the interaction of internal gears, the lifting sprocket drives the lifting chain to rotate, so as to lift and lower heavy objects. Because it is a manual equipment, it depends entirely on the interaction of forces to lift, so the pressure and wear between gears are relatively large.

Because it is made of steel, there is generally no missing teeth, but once the gear is missing, the impact on the chain block is very large, which may reduce the efficiency of construction, or cause the equipment to be unusable and cause safety accidents.