The Greddy RS is sold through many dealers as a blow-off valve. To use it as a recirculation valve you need the adaptors shown on the side and bottom of the valve. See this link for information on the adaptors to 25mm for use in Audi TT and other vehicles.
http://public.fotki.com/mcphill/audi_stuff/engine_and_drivetrain/greddy_type_rs_dive/proto_adapter/