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.
an O-ring, a good fit is critical. O-rings are measured in millimetres. Place the O-ring on a clean, flat, level surface. Determine the inside diameter. Use a ruler to measure from one inner edge to another. To measure the outside diameter, use a ruler to measure from one outer corner of the O-ring to the other outer corner. Measure cross section. Place the O-ring into a vernier calliper. Lightly clamp the jaws of the calliper onto the O-ring, but do not compress it. Record the thickness of the ring (the cross section). If you only have 2 of the O-ring diameters then you can determine the third diameter with the following equations: Measurements: Outside Diameter (OD) = Inside Diameter + (2 x Cross Section). Inside Diameter (ID) = OD - (2 x CS). Cross Section (CS) = OD - ID, Ã· 2. If the o-ring is cut, measure the cross section (thickness) of the O-ring and the length. Converting Length to Inside Diameter: Length Ã· 3.142 = circumference. Circumference - CS = ID.