A rotary encoder includes two component groups that are rotatably arranged relative to each other about an axis. The second component group includes a shaft having a central bore hole, a shoulder and a ridge having an outer surface, and a ring element having an inner surface and an actuation device. In addition, the rotary encoder has a component, which is arranged between the outer surface and the inner surface of the ring element. Both points on the inner surface of the ring element as well as points on the outer surface of the shaft have different distances with respect to the axis such that, via the actuation device, the ring element rests on the shoulder so that a radial force acts on the ridge via the component and a machine part is clampable.