are formed in front walls 80 and extend slightly into side walls 78 referring to fig8 body 70 further includes an end wall 88 that extends between side walls 78 and is joined to one end of stem 72 referring to fig6 and 8 end wall 88 includes a series of pads 92 which provide a convenient bearing surface for abutting engagement with the upper end 54 of upright member 46 as will be seen with reference to fig1 and 12 as shown for example in fig8 front walls 80 do not extend to end wall 88 but rather are abbreviated so as to form windows 96 exposing the upper ends front walls 80 the windows 96 extend to the hollow interior 76 of body 70 referring again to fig5 recesses 84 form a raised separator portion 102 separating the channels or recesses 84 from one another in the preferred embodiment separator 102 comprises the central portions of side walls 78 as can be seen in fig9 recesses 84 are preferably continuous with windows 96 to allow for easy threading and assembly of the tether members as will be described below referring to fig9 end wall 88 preferably defines a downwardly facing recess 106 defined by side wall 78 and locator walls 108 referring now to fig9 and 10 webs 42 are looped over front walls 80 and secured with stitching as indicated in fig1 the inner portions of the loops surrounding the front walls 80 have edges received in recesses 84 see fig5 and 9 so as to space the looped portion of the tethers from the center portion of the hollow interior of body 70 with reference to.