This 6.5" inside diameter PVC coupling works great keeping wind from blowing into the top vent of the smoker and from creating a stronger draft out of the smoker from wind blowing across the top vent. It's heavy enough and round to hold its own in the wind but not too heavy to rest on the therm cables. I didn't want to go down through the coupling incase it got knocked off, taking the therms with it. It's plenty wide and open at the bottom in the back and side of the smoker to not create a draft through the smoker since I don't need it with the mailbox mod.
-Kurt
-Kurt