Abstract: The present invention is directed to a connector that includes a base surface having a front end and a back end; an upper surface sloping at one end to connect with the base surface at the front end; and a third surface connected between the back end of base surface and the other upper surface, wherein the third surface has a lower end substantially perpendicular to the back end of the base surface, and an upper end joining the other end of the upper surface, as well as a curved section between the lower end of the third surface and the upper end of the third surface, in addition to a substantially flat section between the lower end of the third surface and the curved section of the third surface, wherein the curved section of the third surface is substantially contiguous with the upper end of the third surface.