Zipper in the process of the open or close, pull head is straddles the chain belt, chain belt along the length direction of movement, its sliding, and so did the tooth chain with each chain "meshing and separating" (pull head with initiative); Separated from zipper mesh and the movement of the process, the pull head is always a certain fixed point on the structure and moving chain tooth tail made contact, change of chain tooth contact point is the constant is head of a fixed point on the structure, as a result, the mesh point determines the plastic zipper wholesale and smooth degree of the separation process, the quality of the zipper pull and meshing, it shows that the pull head plays a leading role in the use function of zipper is of great importance.