although the connector 22 illustrated in fig2 8 has two projections 40 adapted to extend into indexing holes 20 in a vertical support column 12 any other number of projections 40 can instead be employed for this purpose for example a single projection 40 can extend from the central wall 24 for insertion into an indexing hole 20 in a vertical support column connectors 22 having such a configuration can be useful for connection to vertical support columns 12 each having only a single indexing hole 20 into which a projection 40 can extend at any given height along the vertical support column 12 alternatively such connectors 22 can be coupled to other vertical support columns 12 each having two or more indexing holes 20 at a given height along the vertical support column 12 as another example the connectors 22 in some embodiments have three or more projections 40 extending from the central wall 24 the projections 40 extending from the central wall 24 in the illustrated embodiment are located at substantially the same elevation when the connector 22 is coupled to a vertical support column 12 as described above however projections 40 can extend from different vertical positions when the connector 22 is coupled to a vertical support column 12 the projections 40 of such connectors 22 can be received within two or more indexing holes 20 located at different vertical positions on the vertical support column 12 in the embodiment of the present invention illustrated in fig1 8 a cross brace 14 is received within and is supported by the connector 22 however.