There really is none. I just felt with the top ported burner less heat went out the sides and was faster at heating the flavorizer as the heat went directly into itLarry, how is the difference obtained, going by a thermometer or cooking a item ?
All you should need is that middle one. You can mix that with any other outer burner tubes. I'm pretty sure the plastic spider guards go on the newer style tubes as well.I need to see what I have left. I am not sure I even have one more full set of the early ones that are capable of being restored. Even 304 stainless eventually goes to pot over many years of use!