These thumbscrew window locks are constructed of heavy-duty extruded aluminum, and each come with a steel thumbscrew. Window locks like these are designed for use on older style horizontal and vertical sliding windows, manufactured with metal frames. The locks fit over the window frame fins and the thumbscrew locks into the outer face of the fin, which can be no thicker than 3/16 in. Other versions of this lock are available with non-marring shoes, with larger/thicker frame fin capacity, with dual thumbscrews for double the holding power, and with single and dual Allen head set screws for tamper-resistant installations.