Self-locking bolt drive mechanism

A lockable drive device has a pull rod 2 which moves across the back of the face plate 1 between an unlocked and locked position. A rotatable entraining member 5 engages with a toothed engagement means 4 attached to the rod 2 to cause the rod 2 to move. In the operated position (fig. 2) the entraining member is engaged with the engagement means such that any force applied longitudinally of pull rod 2 is transferred radially along the entraining member through its pivot axis. Thus such forces eg to force a bolt attached to the pull rod, will not cause rotation of the entrainment member and consequent release of the bolt. In the specific embodiment the device is associated with the bolt of a window or door fastener.