Hart & Cooley 3PSV12 Pellet Vent Pipe 3 x 12 in.

Lock-Ring style connection.
3" to 12" pipe and fitting couplers overlap 1-3/8" when joined together; therefore, assembled length is 1-3/8" less than listed length.
The allowable minimum clearance to combustibles is 1"
Outside Diameter (OD) Sizes 3" through 6" is size plus 1/2". Sizes 7" through 12" is size plus 1"
A full set of installation instructions are supplied with caps and supports.