A finger (14) includes a pair of overhanging portions (16, 18) that project out laterally from a main body portion (20). Outer peripheral surfaces of the overhanging portions are made up from five surfaces including upper surfaces (16a, 18a), side surfaces (16b, 18b), lower surfaces (16c, 18c), first end surfaces (16d, 18d), and second end surfaces (16e, 18e). Crowning is applied to the intersections between these surfaces.