O-Rings function primarily as gaskets that seal connections between structures like pipes and tubes or within pistons and cylinders. They’re typically made of pliable materials like rubber or high-quality PTFE. When pressed between two mating surfaces, they effectively block the passage of liquids or gases.
Whether a PTFE or rubber seal, metric o-rings come in two main forms: static or dynamic. A static seal is where the ring remains stationary and is used simply for containing pressure or maintaining a vacuum. Dynamic seals can be either reciprocating (for use in pistons and cylinders) or rotating (for applications in which a shaft rotates inside a housing).