This specification and part standard covers polytetrafluoroethylene (PTFE) resin material and the dimensional requirements for scarf-cut retainers (back-up rings) previously covered by MIL-R-8791 and MIL-R-8791/1. The retainers are intended for use in hydraulic and pneumatic system components as anti-extrusion devices in conjunction with seals and O-rings. Use Retainers to the dimensions in this specification are for use in glands to MIL-G-5514 (not for new designs) They shall not be used in glands to AS4716 or AS5857@ please refer to the Caution Note below. CAUTION: Parts standard AS5781 for use in AS4716 glands and parts standard AS5860 for use in AS5857 glands have been published. Backup rings to AS8791 shall not be used in AS4716 or AS5857 glands.