the fourth vertical bar 11 is pivotally and slidably attached to the fourth primary cross bar 15 below the point at which the third and fourth primary cross bars 14 15 are pivotally attached to each other the top end of the fourth vertical bar 11 is fixedly attached to a second extension piece 20 a which in turn is pivotally attached to the second horizontal arm 6 a the first and second primary cross bars 12 13 each has a bottom end and a top end the bottom end of the first primary cross bar 12 comprises a foot piece 21 the top end of the first primary cross bar 12 is pivotally attached to roughly the center of the second vertical bar 9 similarly the bottom end of the second primary cross bar 13 comprises a foot piece 21 the top end of the second primary cross bar 13 is pivotally and slidably attached to roughly the center of the first vertical bar 8 and pivotally attached to the top end of the second secondary cross bar 17 this is shown better in fig4 the first and second primary cross bars 12 13 each comprises a middle third for example if each primary cross bar were divided into thirds length wise there would be a top third a middle third and a bottom third and the first and second primary cross bars 12 13 are pivotally attached to each other in the middle third of each primary cross bar the third and fourth primary cross bars 14 15 each has a bottom.