Yup, get that alot at the auto parts stores too!
My advice would be stay far far away from Home Depot / Lowes & buy some good 316 stainless pipe online.
Here is my pipe that I bought @ Home Depot after 1 season of burning coal & 6 months in a damp basement:
After that, I bought some Heat-Fab 304 stainless chimney liner as my stove pipe:
That even ended up with some small pinholes from corrosion. If I were to do it again, I'd spend the extra $$$ for the 316.
Jack Magnum wrote:...what is better for the outside piping ,double or triple wall pipe ?
The number of walls dictates your clearance to combustibles: If nothing is within 18" of the pipe, use single wall. Double wall ( if I remember correctly ) needs only 2"-3" clearance, & triple I would guess would be even closer.
For going through a wall, I would get as many walls as they make! Not that a coal fire gets that hot, but you have to think worst-case scenario -- like if the wife doesn't remember to close the ash door on the stove & runs out shopping....
One thing I forgot to mention about using chimney liner -- sometimes the elbows don't fit as nicely as the black stovepipe. You have to be patient & aggressive with putting them together. Mine was a royal pain in the ass. Once I got it together, I left it together -- even to clean. Saves many headaches