Abstract: A housing with a top wall, upstanding parallel walls and two upstanding posts between the upstanding walls on a line parallel with the walls. Each post extends through an elongated opening in a first bolt which is mounted slidingly in the housing for reciprocation toward first and second ends of the housing. The bolt is extendible beyond the second end of the housing for engaging a window jamb when the housing is mounted on a sash of a tilt window that is fully seated in the jamb. The bolt is urged toward the second end by a spring in one of the elongated openings, bearing on the bolt and the post in the opening. A second bolt is supported slidingly between the first bolt and one of the walls, and is extendible beyond the second end for engaging the jamb. A portion of the first bolt extends through an upstanding wall, and a portion of the second bolt extends through the top wall.