Abstract: A magnetic coupling assembly for selectively rotating rollers of a roller conveyor when the torque required to maintain this rotation does not exceed a predetermined threshold is described herein. The magnetic coupling is mounted to the side rail of a conveyor, below the conveyor rollers and include a driving portion rotatably mounted to the side rail and a driven portion rotatably mounted to the driving portion. Corresponding friction surfaces of the driving and driven portion are brought and maintained in contact via a magnet and an element made of magnetic material or another magnet. Means for varying the distance between the magnet and the element made of magnetic material are disclosed. The present invention is also concerned with means for simultaneously adjusting more than one coupling assembly and with means for detecting the rotation of conveyor rollers.