A Y-channel and a wedge
What Actually Joins a Zip?
The slider is two simple machines: a Y-channel that hooks teeth together and a wedge that prises them apart.
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Step 1 of 5
The teeth are hooks, not a straight edge.
Each tooth has a bump on top and a dimple beneath, so a closed zip is really every tooth locked into the two teeth opposite it.
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Step 2 of 5
Closing is a Y-shaped channel.
Two separate rows enter the wide top of the slider and are guided steadily inward until they are pressed together and interlock at the narrow end.
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Step 3 of 5
Opening uses a wedge instead.
Running the slider the other way drives a small blade between the two rows, prising each pair of teeth apart in turn as it passes.
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Step 4 of 5
Both directions are the same machine.
Nothing inside the slider changes. Which of its two shapes does the work depends entirely on which way you happen to be pulling.
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Step 5 of 5
A single bent tooth ruins the whole zip.
A tooth that will not seat leaves a gap, and because each tooth relies on its neighbours, everything past that point fails to hold too.
A jacket zip has around 100 teeth, and every one of them has to hook correctly for the zip to hold at all.
The short version
A zip works because the slider is a Y-channel that forces hooked teeth together one way, and a wedge that prises them apart the other.
Try it yourself
Open a zip slowly and look inside the slider. You can see the little wedge pushing down between the two rows of teeth.
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