The sinuses are air-filled cavities. 1  They are located: 2  Within the bony structure of the cheeks. 3  Behind the forehead and eyebrows. 4  On either side of the bridge of the nose. 5  Behind the nose directly in front of the brain.
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 most common types of rubber o-rings include viton o-rings, teflon o-rings, neoprene o-rings, silicone o-rings and nitrile o-rings. Some of these plastic materials create clear o-rings, particularly the silicone base. The food and medical fields use the clear o-rings often. Metal o-rings are also widely available. Nitrile O-rings are by far the most popular type of seal material used in the world. 2  Nitrile o-rings are carbon triple-bonded to nitrogen, which provides good resistance to oils and fuels. 3  O-ring kits are sets of o-rings that are designed to replace faulty o-rings.