The basic frame (1) consists of angle pieces and flat steel. The support frame has a tread pedestal (2) pivot-mounted on it. The middle strut of the tread pedestal has a support (3) rotatably fixed to it by plug-in bolts so that the support can safely slide along the support frame. The pivot bearing (5) contains a torsion spring for moving the tread pedestal up and down. A plate spring has a locking bolt (7) welded on.
