i used 4" truck exhaust for the stack and 5" for the fb inlet. it was free and works nice. I used rain hats for the dampers. i wasn't sure at first, but they are working out ok so far, and they were also free.
I will look around until I can find some stuff, even if it is too thick, I will use it any way. Like Frank said as long as it is the right size thickness doesn't matter. That sounds a bit funny.
Current Smokers: Backyard RF Offset and Hybrid RF Offset trailer rig with Cowboy cooker and fish fryer, always room for more........