O-ring

O-rings are circular cross-section rubber seals, named as such due to their O-shaped cross-section, also known as O-ring seals. They first appeared in the mid-19th century, initially used as sealing components for steam engine cylinders.
Due to its low cost, simple manufacturing, reliable functionality, and straightforward installation requirements, the O-ring is a common sealing mechanical design. The O-ring can withstand pressures of several tens of megapascals (thousands of pounds). It is suitable for both static applications and dynamic applications involving relative movement between parts, such as the shaft of a rotating pump and the piston of a hydraulic cylinder.