The
Zipper
Two rows of tiny hooks, and one small slider that makes them hold on to each other.
Two rows of tiny hooks, and one small slider that makes them hold on to each other.
A zipper is two strips of fabric tape, each with a row of small teeth. On their own, the rows do nothing. The trick is where each tooth sits.
Every tooth has a bump on top and a hollow underneath. The two rows are offset by half a tooth, so each bump lines up with a hollow on the other side.
The slider has two openings at the top and one at the bottom. Inside, its walls press the two rows together at just the right angle. A small wedge sits between the top openings.
As the slider moves up, it presses the rows together, and each bump snaps into the hollow of the tooth across from it. Once they're locked, you can't pull them apart sideways.
Going down, the wedge pushes between the rows and tips each tooth back out of its hollow, one at a time. Unhooking them one by one takes very little force.
Grab anywhere on the zipper and move it up or down.
Look at the teeth just above the slider. They come in at an angle. That angle is what lets each bump slide in over the edge of the tooth next to it. If you pushed the rows together flat, they wouldn't hook.
Whitcomb Judson patents a "clasp locker" for shoes. It jams easily and never really catches on.
Gideon Sundback is granted a patent for the "separable fastener", the bump-and-hollow tooth design that zippers still use today.
The name came from B.F. Goodrich, who sold rubber boots with these fasteners in the 1920s and named them after the sound.*
* This is the usually told origin of the name. The trademark history is well documented, but "named after the sound" is the story as it's usually told, not something on record.
Sources: US Patent 504,038 (Judson, 1893); US Patent 1,243,458 (Sundback, "Separable Fastener", 1917).