Here's some good information I found on a website called BlueInGreenSoHo.com about chain stitching. Seem the people there know their stuff, and worth a look.
What's in a stitch?
When you buy a pair of jeans at Blue in Green, they will hem them for free. All hemming is done with a vintage Union Special 43200G chain stitcher, the same machines that hemmed the original American work wear of yesteryear.
So, what's a chain stitch? A chain stitch is the type of stitch you see on the hem of premium jeans. It is made of two threads chaining and locking together for superior strength and flexibility. It's much stronger than a regular single stitch. When you cuff a pair of premium jeans, a beautifully stitched chain-stitch is the perfect compliment to a nice double-selvage outer seam. . . .
Why use a Union Special machine?
Union Special sewing machines were the machines that constructed the original jeans of old. These vintage machines are still some of the strongest machines out there and are highly sought after by jean aficionados worldwide. Because of the unique characteristics of the machine, it has a special "pull" to the fabric while stitching, this creates a slight directional pressure in the hem. As the jeans shrink after several washes, this tug will develop a pronounced "roping" effect in the hem. This effect is most pronounced when the hem is stitched with a vintage Union Special chain stitch hemmer machine.
When possible they apply the same thread used by the manufacturer for sewing the jeans and match the color as close as possible to the thread used in the original hem. They go to great lengths to match the color, weight and texture of the thread, even if the original chain stitch uses two different color threads. The end result is an exact reproduction of the original hem.
They also offer hemming for online orders, just make your request when checking out in the "Customer Note" section.
Tomorrow I'm off to the slopes for a week of snowboarding and cross country skiing. It'll be my second time trying it. Hope I don't seriously injure myself. At least there's some good snow already. Kläppen.se