Twin-Sphere also provides a greater flexibility protecting mating flanges, especially PVC and fiberglass types. The steel flanges easily rotate on the bellows which makes it easier to line up the bolt holes during installation when mating flanges are out of line. They are also available with optional parts such as control rods, rings and control unit plates. Available in EPDM, Nitrile and Viton with flanges in either 316Stainless Steel, Mild Steel or Zinc Plated. Standard flange sizes are ANSI, Table E/D and DIN.