a clutch mechanism for releasing a frictional connection in a double gearwheel drive of a sheet - fed rotary press wherein a gearwheel ring is mounted concentrically on and frictionally connected to a main gearwheel by a spring biased annular clamping element , the clutch including an annular actuator mounted on the press in alignment with but normally out of contact with the annular clamping element and the double gearwheel and means for selectively engaging the actuator with the clamping element and causing relative axial displacement thereof to overcome the spring bias and free the gearwheel ring from frictional engagement with the main gearwheel . the actuator may include an annular fluid pressure cylinder , a camming mechanism or an electromagnet for causing the relative axial displacement of the annular clamping element .