Full definition
A sealing element with a toroidal (donut-shaped) geometry and circular cross-section — the technical name for what is universally known as an O-ring. The term "toroidal seal" emphasizes the geometry: when compressed in a rectangular groove between two mating surfaces, the circular cross-section deforms to fill the gap, creating a reliable seal through both material compression (squeeze) and system pressure (which pushes the elastomer against the groove walls). The toroidal shape provides several advantages: self-centering in the groove, sealing in both directions (bidirectional), simple groove design (rectangular), compact size, and wide availability in standard sizes (AS568 dash numbers in inches, ISO 3601 in metric). Cross-section diameters typically 1.0-7.0 mm. The O-ring is the most widely used seal in the world, specified in millions of applications from hydraulic cylinders to consumer products. Materials: NBR (most common — oil resistance), FKM (chemicals/heat), EPDM (water/steam), silicone (temperature extremes, food), and FFKM (universal chemical resistance). Per AS568B and ISO 3601 for dimensions and tolerances.