The 100316305 Over Pressure Ring fits over the outside diameter of a NW40 flange centering ring O-ring to retain the O-ring when the system is used at internal pressure up to 75 psig. It is made with 304 stainless steel. Series 31 ISO-KF vacuum components are designed for use at subatmospheric pressure and use standard interface dimensions defined by the International Standards Organization (ISO) allowing them to be interchangeable with other ISO-KF compliant components. Series 31 components can be used as modular building blocks to create vacuum piping systems. IS-KF flanges are "sexless" with a symmetrical seal so that so that components are rotatable. ISO-KF vacuum flanges are joined by inserting a centering ring between the two flange faces, and securing them with a flange encompassing clamp.