of the article support portion 16 of the base portion 12 while the top is open by means of a passage through the otherwise closed top portion 32 of the larger column support structure 24 surrounding the receptacle 22 it will be noted in fig1 through 3 that the article support column receptacle 22 extends upwardly past the top surface 32 of the surrounding column receptacle support structure 24 this upward extension 46 serves at least two purposes 1 it provides access to a locking pin or bolt 48 fig1 and 2 which is used to secure the lower end 20 of the article support column in place in the receptacle 22 and 2 it provides additional height and therefore leverage and strength for the article support column receptacle 22 additional reinforcement webs 50 may be provided at the upper corners and or elsewhere about the top of the receptacle 22 as desired the upper portions of the two opposite sides 38 and 40 of the receptacle 22 each include a corresponding series of holes e g holes 52 52a and 52b therethrough for accepting the locking pin 48 to secure the lower end 20 of the article support column 18 at the desired angle the holes 52 are preferably located to position the article support column 18 at a predetermined angle depending upon which hole 52 through 52b is used to secure the lower end 20 of the column 18 in fig3 the first hole 52a secures the column shown as column 18a in broken lines generally vertically relative to the base plate 12 while the second or central hole 52 secures.