Question: what is the difference between a #3 and a #5 zipper?
Answer: The second number, preceded by an actual number sign, tells you the width in millimeters of the chain. So a #3 zipper has a 3mm wide chain, and a #5 zipper has a 5mm wide chain. The #3 will be more flexible than the #5, but not as strong. Now we can break down the name of a zipper and know what it means.