FIG. 2C is a front view of the spacer of FIG. 2A. [0011]FIGS. 3A and 3B are an end and a perspective view of yet another embodiment of the spacer of the invention. [0012]FIGS. 4A and 4B are an end and a perspective view of still another embodiment of the spacer of the invention. [0013]FIGS. 5A and 5B are an end and a perspective view of yet another embodiment of the spacer of the invention.