The center adopts high strength calcium sulfate as the base material, the upper and lower are coated with galvanized steel plate and extended to the sides around, through the form of hook link, stamping, riveting form into a closed ring! Six sides of galvanized riveted sheet, four corners with or without corner keyhole, surface of popular science carpet, PVC or other materials; The bracket is molded with plastic pad on it, and the supporting structure around the beam or the supporting structure at the four corners can be used.