This specification covers virgin, unfilled, polytetrafluoroethylene (PTFE) in the form of molded rods, tubes, and shapes. This specification does not apply to product over 12 inches (305 mm) in dimension parallel to the direction of applied molding pressure, rods under 0.750 inch (19.05 mm) in diameter, and tubes having wall thickness under 0.500 inch (12.70 mm). These moldings have been used typically for parts such as, bushings and insulators, requiring chemical inertness and good mechanical and electrical properties up to 500 °C (260 °F), but usage is not limited to such applications. For applications such as bearins, seals, and back-up rings that do not require dielectric properties it is recommended to use AMS 3678/1 Grade A.