What can I say except it works as designed and very strong and durable. I would reconsider though using this in certain craft sewing items, like book or bible covers, since the dual zipper when opened won't allow an opened book to lay flat. If you get a much longer zipper it might be better, but then at the separating zipper end the zipper pull will create a bulge in the book spine area.  I didn't want to find out what damage that would make on my new bible so I just switch the zipper out and used a regular zipper instead.