To join 2 surfaces of different levels. Carpet-to-tile carpet-to-hardwood low pile to high pile carpet. Screw nails included. Aluminum material with multiple finish options. Carpet metal installation on concrete surface suggestion: Drill a hole in the concrete insert a 3/16 x 1-1/4 or 1/4 x 1-1/4 wood dowel. Use the screw nails provided with carpet metals insert into dowel expanding the dowel to lock in place. null -