Cold Air Intake Hose Missing

I bought a cold a ir intake from ebay and it was missing one of the hoses. I HAVE A M6 O5 4CYL AUTO. The hose I am talking about goes from the back of the engine and connects to the main intake tube. Sorry for the vague description. Does anybody know what size I need? The hose seems like it would need to taper but from other kits I have seen that does not seem to be the case. I think I may need 3.5 mm but that seem kind of small since the connection to the main tube is about .5 inch in diameter. Thanks for any help. Dave