This specification covers a butadiene-acrylonitrile (NBR) rubber in the form of molded rings. These rings have been used typically for at temperatures as low as -55 degrees C (-67 degrees F) where resistance to fuel is required, but usage is not limited to such applications. The cross-section of such rings is usually not over 0.275 inch (6.98 mm) in diameter or thickness. Each application, however, should be considered individually.