An O-ring is a type of mechanical gasket in the shape of a torus. It is similar to a rubber washer only it has a round profile if viewed in cross section along with the small torus shaped protrusion located on the outside and inside diameter. It is a loop of elastomer designed to be seated in a groove and then compressed during assembly between two mating parts. It can be used in stationary applications as well as dynamic applications where there is relative motion between the parts and the O-ring. Examples of dynamic use are hydraulic cylinder pistons and rotating pump shafts. They are one of the most common seals or gaskets used in the design of machinery due to their low cost, reliability, easy installation and able to withstand thousands of psi pressure. A successful joint requires a solid mounting that applies a predictable deformation to the O-ring. O-rings are manufactured in various sizes either in metric measurements or in inch sizes.