This specification and part standard covers polytetrafluoroethylene (PTFE) resin material and the dimensional requirements for retainers (back-up rings) previously covered by AS8791 and AS8791/1 which superseded MIL-R-8791 and MIL-R-8791/1.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 packings and O-rings.