LOCK CYLINDER AND REVERSIBLE KEY WITH KEY-WITHDRAWAL DEVICE

The invention relates to a key-withdrawal block for a reversible key which can be introduced into the key channel of a cylinder core mounted in a rotatable manner in a lock-cylinder casing. Said key-withdrawal block is characterized in that the cylinder-core head has arranged behind it an annular disc (1) which is retained at a fixed location, such that it cannot be rotated, in the lock-cylinder casing and has at least one axial, groove-like cutout (3) on the inner circumference, in that the key, on its shank (2), has mutually opposite grooves (6) which extend in the axial longitudinal direction and of which the dimensioning corresponds with the groove-like cutout (3) in the annular disc (1), and in that the key is arranged in the key channel such that the rotary path of its axis of symmetry (5) running in the key shank (2) is spaced apart from the axis of rotation of the cylinder core, wherein the distance which gives rise to eccentricity of the rotation of the key in relation to the axis of rotation (4) of the cylinder core is smaller than the depth of the groove-like recess (3) on the disc (1).