A ring binder mechanism for retaining loose-leaf pages has a housing, hinge plates, and ring members mounted on the hinge plates for retaining pages on the mechanism. The housing includes a plastic upper housing element and a lower housing element underlying the upper housing element. The lower housing element may be a single piece or multiple pieces. An actuating lever may be pivotally mounted on the housing for engaging the hinge plates and pivoting them to selectively move the ring members between an open position and a closed position.