Chimney pipe ID / double or single wall?

[nickmealey]

Hey there,

I'm rebuilding an old shop and I have some existing sections of chimney pipe that I was hoping to get identified. It's a 6" pipe. I've tried to find any kind of markings but haven't seen any. Maybe clean off the instead and really hunt for some? There are 8 "fins" on each section, if that's helpful.

I'm also trying to decide if it's worth going for a double or single wall pipe going up to the roof (which I need to buy). My stove is fairly small and the height to the roof peak is around 11-12ft (depending on position relative to the peak). It would go directly from the stove to roof within the interior of the shop. The shop is uninsulated and was hoping to get something in there to help keep it warm while working. I was reading that double wall can have better draft but it seem single wall would transfer more heat into the space. Curious about that.

Appreciate any help offered!