The length of the explosion -proof hand stretching zipper, the standard is that the length of the zipper is 0.5 meters shorter than the length of the heavy chain, so that the workers are convenient for operation. It can also be extended or short according to the requirements, but you need to pay attention to check the chain before using it. In particular, the lifting chain of the dual chain and multi -chain should be smooth. Pay attention not to flip the hook. Otherwise, it will cause damage to the gourd.