The screw (1) has a worm shaft (6) rotatable around a vertical rotational axis (2). A worm thread (3) helically extends around the worm shaft. The thread includes a thread initial edge (4) at a both sided initial portion. The thread initial edge is arranged transverse to a rotational direction. An auxiliary wing (7) is arranged offset to the thread initial edge in the rotational direction, and radially outwardly extends from the shaft. The wing includes a driver stump fastened at the worm shaft, and a wing casing detachably fastened at the driver stump.
