This secondary lock is constructed of aluminum and is used to lock your window in an open, ventilating position. It can fit up to a 1/8 In. wide rail. Comes in a painted white finish. Extruded aluminum lock with steel thumbscrew used on metal horizontal sliding windows. For heavier-duty locks see item no's U-9800, U-9802, U-11127, U-11128, U-9810 or U-9812. Finish by tightening thumbscrew with pliers to securely lock windows in closed or ventilating positions. For non-marring locks see no's U-9820, U-9821, U-10876 and U-10551. For vinyl windows use U-9809 or U-10547.