of the props 32 32 1 32 1 32 4 so that the props 32 32 1 32 1 32 4 can each be plugged into one of these tubular supports of the starting members 27 the starting members 27 are usually provided with a spindle and a spindle nut screwed thereon whereby setting of the height or level of the props 32 32 1 32 1 32 4 can be achieved each starting member 27 here has an apertured disc 30 provided with passages the latter serve for wedge fixing to the tubular supports of so called horizontal rod elements 24 25 particularly longitudinal rails and transverse rails provided with connecting heads these connecting points are also termed connecting junctions 29 29 u2032 longitudinal rails 24 and transverse rails 25 are usually used as rod elements the longitudinal rails 24 and the transverse rails 25 are in that case respectively wedge fixed in pairs to the tubular supports of the starting members 27 in such a manner that a stable rectangular base frame is constructed from two parallel longitudinal rails 24 and two transverse rails 25 which are arranged perpendicularly thereto but parallel to one another starting from this base frame which is then constructed in a substantially horizontal plane the.