Such luggage zipper teeth mixed by two rows of chain,relying on the chain tooth bite and closed effect,cross bits is strong,but if the longitudinal stress,two rows of chain zipper teeth up and down easily,present small openings,relying on the small opening,easy to pull zipper.The quality of the zipper is related to the raw material and width of the chain teeth.The zipper is a double open connection,which is composed of many interlaced and precise teeth,and the occlusion is formed to form a closed state.Some of the inferior zippers,the gap between the teeth is bigger,insert the sharp pen head into the zipper,cause the teeth of the zipper teeth the mismatch,so the zipper split,so it is easy to pull apart.Nylon zipper raw material is soft,the stress is the most easy deformation dislocation,Metal zipper material is relatively hard and relatively safe,A narrower zipper is easy to be pricked by the longitudinal force,and the wider zipper is relatively easy to poke.