Product review (3 stars): Nice, but did work for 8" flue.
My wife purchased this for an 8" flue, but the tension arms on the back were too short to apply any pressure on the inside of the pipe. I ended up creating a ring from some aluminum flashing and ribbitting it to the back of it, basically turning it into a Tee Cap, which is actually what we should have gotten in the first place.

This is a very attractive product. And normally is wouldn't knock the product for a bad decision on our part. But the description does state that its for a 6" or 8" pipe.