The street Supply hose, 996-106-666-56. If you add one of the adapter hoses sourced from the GT2 parts bin, you can actually make up this hose (thankfully!). The challenge I see is that there is no part number in PET for the metal hose that serves as a joiner between the street hose and the GT2 center radiator adapter hose. McMaster-Carr may be a possibility?