Abstract: A magnetic rotary locking mechanism for locking a plate or sheet-like member by placing it in tension which may be adapted to provide a self-tensioning locking device for securing a printing plate to a printing cylinder in a rotary printing press. The base and rotatable bar each have formed therein a plurality of magnetic strips which generate a plurality of magnetic fields so that the bar magnetic fields are attracted to the base magnetic fields at a first angular position of the bar with respect to the base and are repelled by the base magnetic fields at a second angular position of the bar with respect to the base.