BRIDGE SHOES engineered to allow bridge expansion and flux. A shoe is required under BOTH ends of 4 stringers (total of 4 pairs) for 'Atlas Pratt Truss Bridge System'. (8 pieces would be needed for true authenticity). However, since 4 are not highly visible (the 4 center shoes), a minimum of 4 is required. Cast white metal. Sold two per pack. Measurements: 5/8" wide x 5/8" wide by 1/2" high.