My truck did not have a heater but when I bought the truck it included a spare dash that had the ducts in place and a third duct of unknown origin. All three were the same tube diameter (I am pretty sure) and the one not in the truck measures 1 3/4". Two of the ducts were the same but the other one had the hose connection offset from the windshield discharge end, I presure for clearance of something. Unfortunately I did not keep track of which 2 came installed in the extra dash and which was the loose one. I just received (long time before installing) defrost tubes from Jim Carter and they are 2" diameter but they also include a rubber ring that I believe is intended to fit on the duct to increase it to match the tube diameter.
