wannab
Sr Member
I would say approx. 2" - 2.25".
The correct stuff will definitely be black 'off the shelf'.
Wow, really 2-2.5" that seems too large, I was thinking 1.25-1.5"?
How about something like this? http://www.ducting.com/T_7_SR.html It has the "rubbery wrinkle" quality posted in your pics and metal "spiral helix" reinforcement.
Doug