Cylinder-lock with flat key

For a cylinder lock a flat key comprising a shank having at least one profile longitudinal groove extending from an end thereof to accommodate a rib in a key channel in a cylinder core of the cylinder lock, said shank including fixed key bits adapted to index tumbler pins in the cylinder lock, said flat key in an area of the wide side of the shank including an additional key bit formed from a movable member, said movable, additional key bit being adapted to be controlled by a shoulder in the key channel such that when the key is inserted said additional key bit moves an auxiliary tumbler into a position which allows the cylinder core of the lock to be rotated, the improvement wherein

• the shank is formed with a transverse opening in a lateral wall of said profile longitudinal groove,
• said additional key bit comprises a rolling element movably retained within said transverse opening in said shank,
• said rolling element has a diameter which is greater than the thickness of the material of the shank in the vicinity of said opening such that said rolling element at all times projects laterally beyond said opening on at least one side of the key.