An O-ring is a torus shaped mechanical seal gasket.It is a circular cross-section elastomer ring that is meant to be installed in slots and compressed when fitted between two or more components to establish a seal at the interface.
O-rings are commonly employed in static or dynamic applications where there is relative motion between the pieces and the O-ring. Fluid or gas seals are examples of static applications while Pump shafts and hydraulic cylinder pistons are examples of dynamic applications. Because they are inexpensive, easy to fabricate, reliable, and have simple mounting requirements, O-rings are one of the most utilized seals in machine design. Typically, O-rings are made of NBR, HNBR, EPDM, FFKM, PTFE, and other materials.