" 38a and 38 b are a top view and a side cut-away view, respectively, of the base plates of the embodiment of FIG. 36a; [0062]FIGS. 39a and 39 b are a top view and a side cut-away view, respectively, of the non-magnetic covers of the embodiment of FIG. 36a; [0063]FIGS. 40a and 40 b are a top view and a side cut-away view, respectively, of the tubular stems of the embodiment of FIG. 36a." . . . . .