FIG. 1 shows a bottom perspective view of my claimed design.

FIG. 2 shows a top perspective view of my claimed design.

FIG. 3 shows a side view thereof of which the other side view is identical.

FIG. 4 shows an end view thereof of which the other end view is identical.

FIG. 5 shows a view similar to that of FIG. 1 with parts exploded to show detail.

FIG. 6 shows a cross-sectional view along the line 6--6 of FIG. 4 showing the uniform rectangular cross-section of the U-shaped piece.

FIG. 7 is a cross-section taken along the same lines as FIG 6 showing a second embodiment of my new design, the only difference being the cross-section of the U-shaped portion.

FIG. 8 is a cross-section taken along the same lines as FIG. 6 showing a third embodiment of my new design, the only difference being the cross-section of the U-shaped portion; and,

FIG. 9 is a cross-section taken along the same lines as FIG. 6 showing a fourth embodiment of my new design, the only difference being the cross-section of the U-shaped portion.