Only one wider tape and put the spiral chain on the middle of tape, and sewing be a chain tape.
Then open the teeth and bend overlapping by go through slider became to a single double layer zipper chain tape, joint by slider became to double tape double teeth layer zipper.
The each single zipper chain be requested have interchangeable function.
It have strongest lateral strength could be do open end zipper assembly for luggage and tents. Assembly function development. Good for running twisting.
