An O-Ring, also known as a Packing, or a Toric Joint, is a mechanical gasket in the shape of a torus; it is a loop of elastomer with a round cross-section, designed to be seated in a groove and compressed during assembly between two or more parts, creating a sealat the interface.
The O-ring may be used in static applications or in dynamic applications where there is relative motion between the parts and the O-ring. Dynamic examples include rotating pump shafts and hydraulic cylinder pistons.
O-rings are one of the most common seals used in machine design because they are inexpensive, easy to make, and reliable and have simple mounting requirements
Off-the-shelf availability for standard O-rings: