Abstract: A molded plastic one-piece loose-leaf ring binder for use in binding loose perforated sheets, book pages and the like. A plastic elongated base strip is ridgidified by ribs extending longitudinally thereof, and has paired integral flexible lugs spaced longitudinally on opposite longitudinal sides of the base strip and extending laterally therefrom. The individual lugs each have an integral arm curved along a length of the arm extending laterally away from the corresponding lug and side of the base strip and each curves in a direction back toward the strip. The curved arms have a cross-section thickness greater than the thickness of the corresponding lug so that their curvature is maintained. The curved arms are paired on opposite sides of the strip and are sufficiently rigid as ring-forming elements insertable into holes of perforated sheets and free ends thereof of a pair locked together to define binder rings.