This specification covers a perfluorocarbon (FFKM) rubber in the form of molded o-rings. These sealing rings have been used typically in applications in contact with air or a variety of fuels, lubricants and hydraulic fluids from -15 to +290 degrees C (+5 to 554 degrees F), but usage is not limited to such applications. Each application, however, has to be considered individually. Instances are known when these rings have been used below -15 degrees C (+5 degrees F) and above 290 degrees C (554 degrees F). The cross section of such rings is usually not over 0.275 inch (6.98 mm) in diameter or thickness.