The hidden lock

Student: Zippers move easily when you want to open or close them, but they don't open on their own. Why is that? YKK employee: That's because there's a lock hidden in the slider!
For example, the slider for a pair of jeans (pictured) has a lock pin that catches on the elements when the pull tab is folded down (such as when the jeans are being worn). This prevents the zipper from opening or closing. * A side view of the zipper
But if you raise the pull tab to a 90° angle, the lock pin lifts up and unlocks, so you can open and close the zipper.
YKK employee: Also, there is a type called the automatic slider where pulling lightly on the pull tab will unlock it, even if you don't raise it to a 90° angle. If you don't hold the pull tab, it stays locked. Student: How does that work?
YKK employee: For example with this type, the upper cover on the slider acts like a spring. Holding the pull tab raises the entire thing and unlocks the zipper. Student: You're right! I never noticed that! * There are other types of sliders as well.
YKK employee: Originally, zippers didn't have locks. But this could lead to big problems when wearing clothes, so zippers with locks were developed. Student: Wow, I thought all zippers were the same!
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