Abstract: The sliding windows in the back of the cab of a pick-up truck are vulnerable to break-ins because a thief can pry the panes apart using friction from the pressure of his hand on the panes. The normal clamp is by-passed during this type of break-in. An adjustable-length strut is formed with hook-shaped ends. The hook-ends engage around the outer edges of the sliding panes. A catch on the strut comprises a peg which is spring-loaded into engagement with a notch. When the driver presses the peg, he thereby disengages the catch on the strut, allowing the strut to be set to the length where the hook ends can be engaged to and disengaged from the edges of the panes.