HNBR-GASKETSO-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: it decrees standard sizes for this kind of article and their tolerances; from this standard, it is also possible to deduce tolerances of non-conventional-sized O-Rings. They have a high finish level and can assure both radial and axial seal. They were born in 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 applied anywhere in a confined fluid is transmitted equally and in all directions throughout the fluid; in this way, every inch of the gasket generates sealing force and the higher is the pressure exerted by the housing, the higher is this force. The pressure of the fluid to be retained reinforces the axial and radial forces generated by the gasket housing. In addition to their excellent sealing properties, O-Rings are also simple to mould, easy to mount and maintain and do not require large housings. Based on 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. Standard hardnesses are 70, for what concerns static applications, and 75, as regards dynamic applications; normally, colour black has the highest performances, due to the presence of dark fillers, and for this, it is considered as standard.

HNBR gaskets can be used in many different fields, as they are highly resistant to aggressive fluids at high temperatures, 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.