A locking system has a bolt which is retractable and extendible and can be used on doors or windows where it is carried by the movable leaf and engages in a keeper in the associated frame when the leaf is closed into the frame. Movement of the bolt is controlled by operation of a handle which causes the bolt to move from the retracted to the extended position and back again. The operating mechanism between the drive rod and the bolt causes the bolt to move in a linear path without rotation and when this linear movement is concluded, then to rotate a head at the end of the bolt to engage behind a keeper in the frame to lock the parts together. This prevents incorrect locking of the head if the gap between the leaf and the frame is greater than specified.