US Patent 7353570 Slide fastener chain

A fastener chain, in which fastener elements each formed into a single unit of synthetic resin are attached at a constant interval along opposing side edges of a pair of fastener tapes, a front surface portion and a rear surface portion are provided on the front and rear sides of the fastener element, the surface of the front surface portion is formed into a curved face entirely swelling out circularly and upward while the rear surface portion is formed into a flat plane which is entirely even, and the front surface and the rear surface of the fastener element may have different shapes or the same shape so as to secure a fastener chain having an excellent tactile feel and beautiful appearance.