elongated member 56 which is guided for vertically reciprocating motion by suitable glide means 58 at opposite ends thereof elongated member 56 is made from a hollow box shaped steel member a plurality of cups 60 protrude downwardly from member 56 and each include a suction passage not shown interconnected with the interior of elongated member 56 in order to apply suction force from the plenum defined within elongated member 56 to cups 60 the suction force is applied to the interior of elongated member 56 from a venturi vacuum pump illustrated at 62 which produces a suction force when compressed air is applied to it in the illustrated embodiment the venturi vacuum pump is capable of drawing a vacuum of 27 inches hg at 60 psi input outlet 64 of vacuum pump 62 is connected through a vacuum switch 66 and hence through a flexible hose 68 to the interior of elongated member 56 the suction produced by vacuum pump 62 and connected through elongated member 56 to suction cups 60 provides means for attaching an entire slat 20 to head 38 the suction applied to suction cups 60 is drawn against the flat surface of u shaped channel 24 to produce firm attachment a plurality of guide bars 70 extending downwardly from elongated member 56 prevent shifting of the slat away from the centerline of elongated member 56 linkage 44 includes a pair of elongated members 72 74 which are pivotally mounted to frame 36 by pivots 76 78 a first end 80 82 is attached to extendable portion.