Lock case with an automatically deadlocking latchbolt. The lock must always be equipped with handles, as the latchbolt is only retracted with the handles. The deadlocking is controlled by a snib in the forend. When the snib is in deadlocking mode, the door is opened by turning the outside key 180° or the inside thumbturn 90°. The handles are then activated, and the latchbolt can be retracted. When the snib is in its up position, the lever handles are activated by the key or the thumbturn. When the snib is in its down position, the handles work normally. The lock case is fitted with a feature to prevent the unauthorized use of the snib. The snib is locked to the deadlocking mode by turning a set screw, located below the snib, about two turns anticlockwise by a hexagonal key, until the screw stops and is opened by turning the screw clockwise. The lock case works with the 4690, 4691, LP711, LP714, LP721, and LP731 striker plates (Recommended: 4692 and 4693 for the LC100X). Fire resistance: suitable for fire doors Mortice standard: SFS 5209.