On the end of each support lever (10) opposite to the pivot connection there is at least one downwards protruding running roller (11), a fixing mechanism (14) for detachable locking of the support lever in the swivelled down position, and a locking mechanism (13) for retaining the lever in the not-in-use position. The support levers can be operated independently of each other, or can interact for synchronous movement. A foot contact plate is provided on the upper side of the support lever.
