Redesigned to attach to the fabric in a different way, I think. Usually the teeth are attached somehow to the fabric strip. I think the strip has a ridge at th

Redesigned to attach to the fabric in a different way, I think. Usually the teeth are attached somehow to the fabric strip. I think the strip has a ridge at the edge where the teeth go, and the teeth are clamped over that ridge to hold them in place. Then the fabric strip is easy to sew onto a garment. It looks like the new design has only the ridge, hence it's called a string, and is hard to sew onto a garment.