and a plurality of circular through holes may replace t shaped adjustment holes 58 in vertical post second section 46 in this alternative embodiment the user may align the adjustment rod flange through hole with a vertical post second section adjustment hole and insert the threaded fastener through the aligned holes a nut not shown or other suitable fastener can be used to secure the adjustment rod to the vertical post second portion longitudinal adjustment rod 18 is also preferably formed from extruded plastic or other suitable material and has a generally cylindrical shape a first end 80 a second end 82 and a longitudinal axis 1 it should be understood that any suitable material may be substituted for plastic such as aluminum steel or a carbon composite a t shaped mounting post 84 extends outwardly from longitudinal adjustment rod first end 80 in a direction generally parallel to axis l t shaped mounting post 84 has a flange 86 sized appropriately to slide through a corresponding t shaped adjustment hole flange portion 58 a a web 88 connects t shaped mounting post flange 86 to longitudinal adjustment rod first end 80 and is sized appropriately to fit into the web portion 58 b of an adjustment hole 58 when the user chooses to mount longitudinal adjustment rod 18 to the vertical post second portion 46 mounting post flange 86 slides through adjustment hole flange portion 58 a until adjustment rod first end 80 engages first surface 50 of vertical post second portion 46 the user may then slide the.