Rubber O rings are elastomer materials that are used to seal connections to prevent leaks. The initial classification for rubber O rings is static and dynamic, where static rubber O rings form a seal for two surfaces that do not move, while dynamic rubber O rings make a seal between surfaces that do move.

O-rings are very commonly found in pumps, cylinders, connectors and valves, helping to seal joins between separate parts and prevent leaking of fluids and gases. They're used with static, dynamic, hydraulic and pneumatic components, making them an especially versatile solution to a very widespread engineering issue.