Abstract: A lock and key set in which the lock includes a cylinder rotatable in a barrel which barrel is rotatable to actuate the latch wherein the cylinder incorporates a laterally spring biased bar which includes slots or projections adapted to engage with corresponding slots or projections on the keys so that the bar can be aligned in one of three positions in which its ends are within the diameter of the cylinder or one of each end of the bar projects beyond the cylinder to engage with the barrel. This is applicable to pin tumbler locks and locks of the type in which a latch means is actued by movement of actuating members through associated slots in latch elements there being two sets of latch elements such that when the slots in each set of elements are aligned, the actuating members can pass through. One set of latch elements are positioned by a setting key and the other set are positioned by a corresponding access key.