These are the same machined aluminum injector seats used in Radium fuel rail kits for Subarus. They are required when converting an OEM side feed fuel rail to top feed. They simply "pop" into the OEM side feed injectors bores on the intake manifold or TGV housings. They seal to the machined injector counterbore using the included Viton O-ring. Sold in sets of 4 or 6.
The 26mm injectors seats are for early Subaru engines. They are black anodized, as shown below. 

The 22mm injector seats are for later Subaru engines. They are green anodized, as shown below. 

Measure before ordering. 

Both injector seat styles use the following lower injector O-ring measurements shown above. 

Features

-CNC Machined Billet 6061 Aluminum
-Bright Dip R5 Type-II Anodizing
-Laser Etched Logo
-Viton O-rings