A square (rectangular) ring is a sealing device made in the shape of a torus (circular top view) with a square cross-section (side view). The main reason for using a square ring in a sealing application is that it performs the sealing function superiorly and at a lower cost than any other comparable sealing device. For existing applications, there is no need to change design or procedures. The square rings fit into the O-ring grooves and are interchangeable in size.
Square (rectangular) ring is available in a variety of rubber and plastic materials such as NBR, Viton, EPDM, silicone, etc. In most static applications, a square ring will serve as a direct replacement for an O-ring and will generally perform a high pressure seal function as good or better than an O-ring.