This specification covers virgin unfilled polytetrafluoroethylene (PTFE) in the form of extruded rods, tubes, and shapes. These products have been used typically for parts, such as insulators and bushings requiring chemical inertness and dimensional stability up to 500 °F (260 °C) and better mechanical and/or electrical properties than AMS 3656, but usage is not limited to such applications. for applications such as seals, back-up rings and bearings that do not require dielectric properties and radiographic inspection it is recommended to use AMS 3678/1 Grade B.