Patent ID: 8539803

Claim:
A cylinder lock with a rotatable key plug ( 112 ) having a profiled keyway ( 113 , 116 ), said keyway being configured to accommodate an elongated, substantially flat key blade ( 120 ) having a longitudinal groove ( 122 ), wherein said keyway has two opposite lateral sides, which are substantially parallel to each other, and a profile rib ( 150 ) projecting outwardly from one of said opposite lateral sides into the keyway, said profile rib having a downwardly projecting tongue portion ( 161 ) configured to extend inside said profile groove ( 122 ) upon inserting said key ( 120 ) into said key plug ( 112 ) of the lock, and wherein said tongue portion of the profile rib having a uniform width and extending downwardly from a base portion of said profile rib, down into a lowermost end portion which has two opposite substantially parallel side surfaces and a lowermost transverse end surface which is substantially flat or slightly curved, said lowermost end portion extending downwardly in a direction which is parallel to a central longitudinal plane (A′) through said keyway, said lowermost transverse end surface extending substantially in a plane which is substantially perpendicular to a said central longitudinal plane (A′), and the vertical dimension (h′) of said downwardly projecting tongue portion ( 161 ), measured in a plane parallel to said lateral sides ( 117 , 117 ′, 118 , 118 ′) of said keyway ( 113 , 116 ), is greater than half of the smallest height (w′) of said profile rib adjacent to said one lateral side ( 117 , 118 ) of the keyway, also measured in a plane (A′) being parallel to said lateral sides of said keyway.