O ring, also known as packing, 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 seal at the interface. 

O rings can be produced by many chemical methods, including extrusion, injection molding or pressure molding.

O rings are most commonly used in static applications and dynamic applications, including rotating pump shafts and hydraulic cylinder pistons.

For now, o rings are one of the most common seals used in machine design becuase they are inexpensive, easy to make, reliable and have simple mounting requirements. 

To look for high quality products, please visit http://www.mfc.com.tw/O-Rings.html