bearing plate 125 is pressed into the catch member 120 and snapped into place as shown portions of the bearing plate 125 may be bent or folded to assist in securing the plate 125 to the catch member 120 for example one end 126 of the bearing plate 125 may be folded and press fit into a corresponding recess 121 in the catch member 120 as shown the bearing plate 125 may but need not provide a contoured bearing surface for continuous uniform engagement between the catch member 120 and engaging portion 112 during pivoting of the catch member 120 as described in greater detail above as with the movable block 52 of the embodiment of fig1 3 the exemplary catch member 120 of the present application may also be provided with a sloped or chamfered front edge 128 opposite the bearing surface when the illustrated catch member 120 is inadvertently placed in the post retaining position while the rail member 110 is extended the chamfered front edge 128 allows the post 112 to slip past the catch member 120 for retention of the rail member 110 in the retracted position while the chamfered portion 5230 of the movable block 52 of the embodiment of fig1 3 is provided as a narrow groove in the embodiment of fig4 7 the chamfered edge 128 extends along a greater portion.