Our #9 metal zipper pull tabs in black are quite strong and durable, and are used in many commercial and industrial applications. The number on the back of the zipper slider pull tab is most often tied to the gauge size of the zipper. The gauge size refers to the size of the teeth, as the number gets larger, the teeth get bigger. There are #2, #5, #8 gauge size zippers and go as high as #15. The most common gauge sizes are #4 and #5. The teeth are measured with the zipper closed. If you measure the teeth in “mm”, that will indicate what gauge the zipper is.