Abstract: A lock set comprising a cylinder lock having a stator and a rotatable member rotatable in the stator and having a key slot and at least one side; a security element with protrusions, pivotally connected to the rotatable member; and one or more fitting keys, each having one or more recesses and one or more extensible members. The distances between the protrusions of the security element correspond to locations of the recess(es) and extendible member(s) of the fitting key for engagement therewith, such that using the fitting key will have the security element positioned in a non-obstructing position allowing free rotation of the rotatable member in the stator and using an unfitting key will cause a portion of the security element to protrude from the outer wall of the rotatable member engaging the inner wall of the stator thereby preventing rotation of the rotatable member in the stator.

Abstract: The present invention provides a key blank and a key set. The key blank includes one or more telescopic members inserted through corresponding one or more channels of the key shank for fitting to release a security mechanism of a lock unit. The lock set has one or more fitting keys and a lock unit including: a stator; a rotor; a first locking mechanism; and an additional security mechanism including one or more wafer units. The key shank has one or more telescopic members each inserted in a channel perforated in the key shank. The wafer unit of the security mechanism is located and configured for engaging an edge of the telescopic member when the fitting key is used, such that each telescopic member will move the respective wafer unit it engages for releasing the additional security mechanism for allowing the rotor to rotate in the stator.