Vic-Flange® adapters require a smooth hard surface at the mating flange face for effective sealing. Some applications for which the Vic-Flange® adapter is otherwise well suited do not provide an adequate mating surface. In such cases, it is recommended that a metal (Type F phenolic for Style 641 with copper systems) Flange Washer be inserted between the Vic-Flange® adapter and the mating flange to provide the necessary sealing surface.