O-rings are rubber seals with a circular cross section. Because they have an O-shaped cross section, they are called O-ring seals, also called O-rings. It began to appear in the mid-19th century when it was used as a sealing element for steam engine cylinders.
Because of its low cost, simple manufacturing, reliable functionality, and simple installation requirements, O-rings are the most common mechanical design for sealing. O-rings are subjected to pressures of tens of megapascals (thousand pounds). O-rings can be used in static applications or in dynamic applications where there is relative motion between components, such as the shaft of a rotary pump and the piston of a hydraulic cylinder.