Explainer #1
How does a zipper work?
A zipper is two rows of identical teeth, offset by half a tooth. The slider's Y-shaped channel steers the rows together at a slight angle, so the bump on each tooth drops into the hollow under the tooth opposite and the two rows lock into one chain. Pull the slider back and a small wedge at the top of the channel pries the teeth apart again.
The principle
Interlocking by shape, guided by a wedge. Each tooth has a small knob on one face and a matching recess on the other. Two teeth can only hook together, or come apart, when they are tilted relative to each other, and that is exactly what the slider does: its two inlets bring the rows in at an angle and its channel narrows until they lie flat and locked.
Once the teeth lie flat in a closed row, pulling the two sides apart can’t lift the knobs out of their recesses, so the zipper holds. The only easy way to separate them is to tilt them again, which is the job of the wedge (the “diamond”) at the top of the slider. It works like any wedge: a long, gentle push along the zipper becomes a strong sideways spread.
The modern design with identical interlocking teeth was patented by the Swedish-American engineer Gideon Sundback in 1917.
Common myth
A zipper that splits open has broken teeth
Usually the teeth are fine. When a zipper closes but separates again behind the slider, the slider has most often worn or spread open, so its channel no longer squeezes the teeth fully into each other. That is why gently pinching a worn slider back into shape (or replacing just the slider) often fixes it.How this video was made: 3D animation rendered in Blender from a simplified model: real teeth are smaller and more rounded, but the geometry of knob, recess, half-tooth offset and Y-channel is the same.
