O-Ring Glossary

AF: Air Force
AMS: Aerospace Material Specification
AN: Air Force-Navy
AS-568A: Aerospace Standard Uniform Dash Numbering system for O-rings Clearance
Diametral:The difference in diameters of two surfaces to be sealed
Cross-Sectional Dia (C/S): One half the difference between the ID and OD of an O-ring (W)
Dynamic Seal: An application where an O-ring is to seal two parts which are in motion
Elongation: Percent of stretch before breaking
Extrusion: The extension, under pressure, of a portion of an O-ring into the clearance between mating parts
Face Seal: An application where an O-ring seals in a plane perpendicular to its axis
Flash: Excess rubber left around an O-ring at mold parting lines
Gland: Seal assembly, including O-ring, groove and contacting surfaces
Groove: The recess into which an O-ring is fitted
Hardness: Property usually measured with a Shore A Durometer. A reading of 40 is soft, 90 is hard
ID: The inside diameter of an O-ring
MIL: Military
Modulus: Stress at 100% elongation
MS: Military Standard
OD: The outside diameter of an O-ring
SAE: Society of Automotive Engineers
Seal: An O-ring that prevents fluid flow Set, Compression: Permanent distortion of an O-ring after compression
Squeeze: Cross-sectional compression of an O-ring
Static Seal: An O-ring designed to function between parts having no relative motion, a gasket
Tensile: The pulling strength before breaking, measured in pounds per square inch
W: The cross-sectional diameter of an O-ring(C/S)

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