the lower height adjustment member 18 for a six foot body member 12 and for an eight foot ceiling 78 both the upper and lower height adjustment member 16 and 18 have to be extended about one foot the upper height adjustment member 16 is initially assembled by passing the bolts 92 92 through apertures 65 65 and loosely threaded in apertures 90 90 of the weldnut member 88 such that the distance between the upper support member 64 and the weldnut member 88 is sufficient to pass the rib lips 54 and 56 therebetween the lower height adjustment member 18 is similarly assembled that is the bolts 122 122 are initially passed through apertures 105 105 and subsequently loosely threaded into apertures 120 120 of the weldnut member 118 such that the distance between the lower support member 104 and the weldnut member 118 can accommodate the rib lips 54 and 56 the upper height adjustment member 16 is subsequently passed into the internal channels 22 and 24 of the body member 12 such that as previously indicated the following dispositions are occurring with respect to the upper height adjustment member 16 and the upper part of the body member 12 a the generally cylindrical upper hollow members 60 and 62 are respectively slidably disposed in the side internal channels 22 and 24 such that the external surfaces of the generally cylindrical upper member 60 is in slidable contact with the inside arcuate surface 30 and the generally cylindrical upper member 62 is in slidable contact with the inside arcuate surface 32 b the upper support member 64 is slidably passing through openings 44 and 46 c the inside surfaces of the upper support.