Formerly,  the firing & exhaust tube each had respective part numbers.  Currently the factory is using one part number for both the firing & exhaust  replacement tubes. 
 
OLD  CB/ Coldblocker replacement tubes:

#44028130   7 1/2'  FIRING  ALC tube w/ one 3-hole flange, 3" OD

#44028131    7 1/2' Exhaust ALC tube w/ one 6-hole flange, 3" OD

PART #44028132 is current part.