O-Rings
An O-ring is a round ring that is used as a gasket for sealing a connection.
O-rings are typically constructed out of polyurethane, silicone, neoprene, nitrile rubber or fluorocarbon. These rings are commonly used in mechanical applications, such as pipe connections, and help to ensure a tight seal between two objects.

O-rings are designed to be seated in a groove or housing that keeps the ring in place. Once in its track, the ring is compressed between the two pieces and, in turn, creates a strong seal where they meet. The seal that a rubber or plastic O-ring creates can either exist in a motionless joint, such as between piping, or a movable joint, such as a hydraulic cylinder. However, movable joints often require that the O-ring be lubricated. In a moving enclosure this ensures slower deterioration of the O-ring and therefore, extends the useful life of the product.

O-rings are both inexpensive and simple in design and are therefore very popular in manufacturing and industry. If mounted correctly, O-rings can withstand a very large amount of pressure and are therefore used in many applications where leaks or loss of pressure are unacceptable. For instance, O-rings used in hydraulic cylinders prevent leakage of hydraulic fluid and allow for the system to create and withstand the pressures required for operation.