The Fittings | O-ring w/ Centering Ring, SS (KF25) is a vacuum flange sealing assembly that combines a stainless steel (SS) centering ring with a chemically resistant O-ring, designed for KF25 vacuum connections in distillation and extraction systems. The centering ring holds the O-ring precisely in place during assembly, ensuring a consistent vacuum-tight seal at KF25 flange joints. Suitable for use with Leybold, Agilent, and other vacuum pumps and components that use KF25 fittings. Sold individually; compatible with all standard KF25 flanged connections on VTA and UIC wiped-film distillation systems.