This specification covers two types of 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 length, 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 requiring chemical inertness up to 500 °F (206 °C), and better mechanical and/or electrical properties than AMS 3660, but usage is not limited to such applications. for applications such as bearings, seals, and back-up rings that do not require dielectric properties it is recommended to use AMS 3678/1 GradeA.