The design principles of ISO and KF seals are identical. Each flange face is counter-bored or grooved to receive a metal centering ring with an elastomeric o-ring around its O.D. As with KF, the ISO centering ring both aligns the flanges and holds the o-ring in place.

ISO flanges are limited (by the o-ring's properties) to applications with temperatures between ~0° C and 120–180° C, and pressure from atmosphere to ~10^-8 torr or mbar.