A link has link connecting bores (15) and (16) at both ends thereof and a wear rail (13) disposed between the upper portions of the link connecting bores (15) and (16). Portions near the ends of the wear rail (13) are designed to have a hardness smaller than that of a center portion of the wear rail. Accordingly, the portions near the ends of the wear rail can be abraded more easily than the center portion of the wear rail. Since the portions near the ends of the wear rail, in which the portions are easily abraded, are positioned closer to the link connecting bores, abrasion loss in use is smaller than that of the center portion owing to its structure. So, the difference in abrasion amount makes it possible to lower a level irregularity of the wear rail.