A metal strip including an elongate web and a pair of longitudinal medial lands on both sides thereof, is successively stamped or coined so as to be provided with a series of coupling elements each including on each of its both sides a transverse projection and a pair of longitudinal teeth one on each side of the projection, the projection being higher than the teeth. The projection and teeth are formed from material of the medial lands and additionally from material of a portion extending all the way around the projection and teeth, which is thinned down to a thickness smaller than that of the web. Then, the metal strip is notched along its marginal edges to provide the outer profile of clamping legs, and is severed into individual coupling elements.