12 while rotation in the opposite counterclockwise direction loosens the engagement between these two components as illustrated in fig2 the engagement end 66 of each attachment jaw 64 65 is received within one of the attachment slots 40 44 such that the engagement end 66 contacts one of the attachment lips 30 32 in the initial attachment condition the adjustment member 94 is retracted such that the attachment jaws 64 65 are loose and moveable within the respective receiving cavity 50 in this condition the pair of attachment jaws 64 65 can be slid into the open ends of the attachment slots 40 44 as illustrated in fig3 once the attachment laws 64 65 are received within the attachment slots 40 11 the entire cross support 14 can be slid along the length of the pair of side rails 12 to the desired location such as shown in fig1 once the cross support 14 is in the desired location the user inserts a tool into the cavity 100 formed in tile head 98 of the adjustment member 94 once the tool is inserted the tool can be rotated which causes the threaded shaft 96 to rotate and engage the threads formed along the threaded attachment opening 88 formed in the lower attachment jaw 65 as shown in fig1 when the attachment jaws 64 65 are initially positioned the engagement surface 82 formed on the engagement end 66 contacts one of the attachment lips 30 32 when the adjustment member is rotated to pull the jaws 64 65 together the movement of each of the jaws 64 65 in the direction of arrows 102 causes each of the jaws 64 65 to also move in the direction shown by arrows 105 due to the interaction between the respective attachment lip 30.