If you’ve ever had a pair of jeans hemmed at your local dry cleaner, you may have noticed that they came back looking a little off. Not worse, just… different. That’s because, in all likelihood, your jeans were originally finished with a chain stitch. This stitch can only be done on specific machines—the most famous is the Union Special— that sew with one continuous piece of thread and loop it back on itself using a specially designed looping hook. The specific mechanics are difficult to explain (that’s why there are animations), but the basic idea is that the stitch is linked together by this series of loops, hence the “chain” in the moniker. And unless your dry cleaner decided to invest in a decades-old industrial sewing machine, they can’t do a chain stitch. Which is fine, if you just want your jeans the right length and that’s that.
But, if you’re looking for the more authentic option, the chain stitch is the way to go. For one, it’s the historical standard, so you’re paying proper homage to your denim forbears. Beyond that, the directional pressure created by the loops pulling on the fabric helps create roping, an aging effect where the hem ripples a bit and only the higher sections of denim fade. It’s a small detail, but it’s a great one. And finally, the interwoven pattern formed chain stitching is just plain cool looking. But be warned: One break in the thread and the whole thing unravels. Beauty has its price.