This document has been declared "Stabilized" and will no longer be subjected to periodic reviews for currency. Users are responsible for verifying references and continued suitability of technical requirements. Newer technology may exist. The use of equilateral triangle cross-section hydraulic seal backup rings has been found to improve the life and reliability of high pressure O-ring seals especially for high temperature applications. This Aerospace Information Report (AIR) describes the design and operation of these backup rings, tabulates recommended seal groove and gland dimensions, offers recommendations and suggestions for their installation into hydraulic components, and outlines their advantages and limitations of their use.