AS 568 O-Ring
The Society of Automotive Engineers is the
publisher of AS568 Aerospace Size Standard for O-Rings. US
companies adopt the use of this standard for reference most
commonly. AS568 specifies for sealing applications of o-rings
the inner diameter, tolerances, cross-sections as well as size
identification codes. AS568 is used in industries beyond that of
the aerospace, including automotive and general industrial uses.