Q: Why does my zipper keep jamming halfway up the tape?
A jam that repeats at the same point is almost always positional, while one that happens at random is usually a chain or slider problem. Before replacing anything, separate the two causes so a good zipper is not sent back to the maker.
- Run the slider slowly by hand and note whether the stop point moves when the garment is turned; a moving stop points to tape, seam or pull direction.
- Inspect the teeth from both sides under a light for bent, rolled or misaligned elements at that exact position.
- Check whether the seam allowance, a thick interlining or a stray thread is pressing into the chain near the slider.
- Measure the slider gap with a feeler gauge against the maker's drawing; a gap beyond the stated limit is a zipper defect.
- Test the same slider on a spare length of identical chain to see whether the fault follows the slider or the tape.
If the fault follows the slider, it is a zipper defect and belongs with the supplier. If it follows the seam or the garment, correct the process. Keep the failed sample and photographs, because a jam report without a position is hard to settle.