Video narration
A jacket zipper looks simple, but it’s a clever little locking system. It has two fabric tapes, each with a row of small teeth, or “elements,” along the edge. At the bottom, a starter box and a pin line the two rows up so they can feed into the slider. The slider is the key part. Inside it are shaped channels like a tiny Y. When you pull the tab up, the slider guides the left and right rows into that Y, squeezes them together, and the teeth interlock like two hands clasping. Now the track is closed, and the fabric stays joined. Pull the tab down, and the slider does the opposite: it forces the interlocked teeth to bend slightly and separate into two rows again. The zipper isn’t held closed by the pull tab—it’s held closed because the teeth are locked together all along the track.