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.
FR-S/BRZ/86, Fuel Hanger Plumbing Kit, Stainless Filter
FR-S/BRZ/86, Fuel Hanger Plumbing Kit, Microglass Filter
Fuel Rails, Top Feed Conversion, Subaru EJ