A resilient plate includes a plate shaped body. A through hole is defined in the center of the plate shaped body. A plurality of slots is defined in the plate shaped body and the slots cooperatively surrounding the through hole. Each of the slots includes a first substantially straight slot portion, a second substantially straight slot portion and a third substantially straight slot portion. The second substantially straight slot portion interconnects between and substantially perpendicular to the first and second substantially straight slot portions. The slots are oriented about 90 degrees with respect to each other. The resilient plate further includes a plurality of pinholes defined in the periphery portion of the plate shaped body. The bracket includes a plurality of first positioning pins corresponding to the pinholes. The resilient plate is fastened to the bracket by engagement of the pinholes with the respective first positioning pins.