These are the same machined aluminum injector seats used in many Radium Engineering fuel rails. They are required when converting the OEM fuel injector to aftermarket fuel injectors. They simply press-fit into the intake manifold/TGV injector ports with no modifications required. Using the included FKM O-ring, they seal into the machined injector counterbore preventing vacuum (or boost) leaks. The injector seat bores are designed to be used with a common 14mm lower injector O-ring.