in conjunction with the bottom frame member 40 to form a raceway at the baseline as shown in fig6 in fig3 the raceway element 52 is below the transverse frame member 44 while in fig4 the raceway element 52 is inverted as compared with fig3 and co operates with the bottom frame member 40 fig7 a shows the raceway element 52 in the position it occupies in the belt line position shown in fig3 while fig7 b shows the element in the position of fig4 raceway element 52 comprises a frame member 74 that is essentially the same as the top and bottom frame members 38 and 40 i e all three members are the same the member is channel shaped and is shown in fig7 b with its channel facing upwardly so that its base 74 a confronts the corresponding face of the bottom frame member 40 as it appears in fig4 tabs 74 b are folded upwardly at the ends of the frame member 74 for receiving sheet metal screws that are driven through those tabs and into the respective uprights 34 and 36 of the frame for securing the raceway elements within the frame the raceway element 52 also includes spacer means in the form of a pair of short channel members 76 that extend outwardly from the.