Abstract: A locking mechanism for securing a coupling sleeve on a shaft, comprises a coupling sleeve with a receptacle extending along a longitudinal axis for receiving a shaft, a plurality of locking elements, each of which is received in a radial aperture of the coupling sleeve so as to be radially movable between a locking position, in which the locking elements project radially inwardly from the apertures into the receptacle for engagement in a circumferential groove of the shaft, and a releasing position, and a locking ring, which is axially adjustable between a closed position and an open position relative to the coupling sleeve, wherein in the closed position a locking section of the locking ring engages around the locking elements radially on the outside and holds them in the locking position.