Is the diameter the same as the other end of the duct at the heater? Finding the duct hoses with the two different sizes is the problem. Those vents are reproduced in plastic and usually available on ebay. I can't find the ducts.
I am not sure what size is on the heater box, but theses are an exact match as the factory vents. I just machined a sleeve that will allow you to adapt a smaller size duct if you are running an aftermarket A/C system.
