Why zippers fail (and why it's rarely the teeth)
A zipper has one moving part that matters: the slider. Its Y-shaped channel is a funnel — as it travels, it forces the two rows of teeth into alignment so they interlock and hold.
Teeth rarely break. What wears out is the funnel: every forced pull over a thick seam pushes the slider's walls apart a fraction of a millimetre, until the teeth pass through but no longer get pressed together. The chain closes behind the slider, then quietly splits open.
The three everyday failures
- Stuck slider. Fabric or a thread caught in the channel — or grit and corrosion coating the teeth. Force is the enemy: it rips the tape or bends teeth.
- Slider worn wide. The chain engages, then opens behind the slider. The fix is mechanical: gently crimp the slider back to size.
- Slider off the chain. The top stop is missing or opened up, so the slider ran off the end. It goes back on — then the stop needs rebuilding.
One honest limit: missing teeth can't be regrown. If a tooth is gone or a row is crushed, the chain will never lock there — that's a zipper replacement, a job for a needle and a tailor, not pliers.
Before you start. This is a simulated demonstration, not a photograph of your garment. Zipper sizes differ (check the number stamped on the slider back: #3, #5, #8); never force a jammed slider — that's how tapes tear and teeth bend. We don't cover sewn-in zipper replacement, which needs a sewing machine or a tailor.