HNBR-O-RINGSO-Ring is the most commonly used model of gasket in the world. These articles are circular cross-section rings, identified by two main dimensions: thickness and inside diameter. They are regulated by the international norm ISO 3601, which decrees standard sizes for this kind of product and the related tolerances; from that it is also possible to infer and extrapolate tolerances of non-conventional-sized O-Rings. They have a high degree of the finish and can assure both axial and radial seal. Their birth dates back to 1882 with a water-cock patent by Thomas Edison, which discovered that this type of sealing shape could take a big advantage from the Law of Hydrostatics of Blaise Pascal; in practice, pressure exerted wherever in a confined fluid is transmitted equally and in all directions throughout the fluid; in this way, every squared millimeter of the gasket generates sealing force and the higher is the pressure exerted by the housing, the higher is this force. The radial and axial forces generated by the gasket housing are reinforced by the pressure of the fluid to be retained. In addition to their excellent sealing properties, O-Rings are simple to mould, mount and maintain and do not require large housings. On the basis of the type of housing, another crucial point is the hardness: the lower is this value, the more the O-Rings adapt easily and better to the surface structure of the contact surfaces. Instead, the more the fluid pressure rises, the more it is necessary to have a smooth housing surface and use a compound with a higher degree of hardness. Most common hardnesses are 60, 70, 80 and 90 IRHD. Furthermore, as regards dynamic applications, the most used O-Rings have a hardness degree of 75 IRHD.

HNBR sealings can be used for many different applications, among which we can mention the contact with high temperature and aggressive fluids, like gasoline or engine oil, in addition to the resistance against permanent deformation caused by mechanical forces. This type of compound has also good compression set properties: this feature regards a test under crushing at high temperature (around 150/200°C), which can give an idea of the part sealing capability under these hard conditions.