How A Zipper Works

Zippers can only be manufactured using modern machines, but they are built around two of the oldest and simplest tools in the history of civilization: the wedge and the hook.
A wedge is just an object with a slanted surface. If you push a wedge forward against an object, it will push the object to the left or right. . A hook is a curved piece of material that can be used to grab onto another piece of material. Hooks have been used as fastening devices for thousands of years because they are simple and generally sturdy. When used as a fastening device, a hook is generally coupled with a loop, eye or hollow area, which receives the hook. A zipper track is made up of dozens of teeth, each of which combines a hook and a hollow. The idea is to latch every hook on each of the two tracks into a hollow on the opposite track. The latching mechanism, called the slide, is just a collection of wedges. You can see how this system works in the diagram below. As the slide moves up the zipper, the two teeth strips must enter at a specific angle. As the strips move through the slide, the slide's inclined edges push the teeth toward each other. The strips are offset from each other, so each hollow settles onto a hook in sequence. For this to work properly, each tooth must be exactly the same size and shape, and they all must be perfectly positioned on the track. This would be all but impossible without modern manufacturing technology.
In a well-made zipper, the interlocking teeth form an incredibly secure bond -- it is very difficult to separate the teeth by pulling the two strips apart. But the slide can easily separate the teeth, using a simple plow-shaped wedge. When the slide is pulled down, the wedge pushes against the slanted edges of the hooks, pivoting each tooth off of the tooth below it. Just like that, the zipper tracks are detached.