46 of connector part 40 within the envelope of wall 54 as seen in fig1 whereby wall 54 defining an opening 60 will partially surround an associated hook portion 46 as a corollary of this application of the compressive force f along the major axis 56 tends to expose hook portion 46 the insertion of the coupling member 40 into engaging relationship with a slat 14 is facilitated by applying a compressive force f to the slat along the major axis 20 thereof in a manner that is wholly analogous to that just described in the case of adjusting rod 16 however due to the relatively high ratio of the dimensions of the major axis 20 to the minor axis 22 the ballooning effect of the compressive force f will be considerably greater in the slat than is the case in the adjusting rod accordingly hook portion 46 is almost entirely exposed when slat 14 is under the influence of compressive force f as will be appreciated from fig1 and 11 this permits a corresponding hook portion 46 associated with adjusting rod 16 to couple with a hook portion 46 associated with a slat 14 to thereby form a hinge coupling element 70 as seen in fig1 upon release of the compressive.