The WRX Hybrid valve is designed specifically to bolt straight onto all late model Subaru WRXs and STis from MY01 (MY02 in the U.S.) with no adaptors, extras or modifications required.
The Hybrid design allows the valve to be configured to return a portion of the vented air to the inlet, meaning no more air flow meter problems and a great sound. The kit also includes a blanking cap for the return outlet allowing the valve to vent 100% to atmosphere for maximum noise!
It is a little known fact that the late-model WRX factory blow-off valve is actually designed to leak at boost pressures exceeding the factory level. Replacing it noticeably improves throttle response, and is definitely recommended in applications where the boost has been raised.