AS568

AS568 is a standard specification for O-ring size designation used in aerospace and other industries. It provides a complete system for identifying elastomeric rings by their cross-section thickness (CS) and inside diameter (ID), expressed in inches, with defined tolerances. The standard is published by the American Society of Mechanical Engineers (ASME) as part of its aerospace sealing standards and is maintained through revisions commonly referred to as AS568A, AS568B, and later updates. O-rings manufactured to AS568 can be selected by dash-number designations that encode their CS and ID, enabling designers, manufacturers, and maintenance personnel to verify compatibility with mating parts and glands.

AS568 focuses on size designation and dimensional accuracy; the materials, hardness, and service limits of O-rings are specified by other standards and by supplier data, depending on the application. The standard's widespread adoption, especially in aerospace, stems from its detailed, interrelated size tables that facilitate interchangeability and procurement. While ISO-based metric sizing is used in many regions and applications, AS568 remains a dominant system in the aerospace and defense sectors and for equipment designed to the standard.