From By Annie :These hard-to-find nylon-coil zippers are perfect for bags and carriers. Here's why we prefer them: Dress and skirt zippers carried by most local stores are too small.
The #4.5 size is just the right size for purses, bags, and totes. The wide zipper tape makes insertion easy. Unlike zippers with chunky, molded polyester teeth, these handbag zippers are soft and flexible, making them easy to sew through. (No more broken needles!)
The nylon coil is strong and durable zip after zip. The double slide lets you open your bag from either end.
The double slide also enables you to make two single-slide zippers. For example, if you only need an 18" single-slide zipper for your project, you'll still have a 12" single-slide zipper left for another project