<p>A re-keyable cylinder lock has a control member to permit or restrict transverse movement of a re-keying unit. The control member is movable axially between first and second positions and transversely to a third position from the second position. In the third position, the re-keying unit moves transversely and disengages from first tumbler pieces. A limit member is provided to prevent the control member from moving axially when no right key is inserted into a plug. A security arm is connected to the control member and is breakable so that destructive forces cannot reach the control member.</p>
