This unique Insert Adapter allows for front-to-back and side-to-side adjustment in the firebox. The two-piece design allows the unit to slide to adjust the center distance between collars. The 6 adapter, when fully closed, has a 6" center-to-center measurement and when fully extended has a 12" measurement between the collars. The 8" adapter has a 7" measurement between the centers of the collars and a 12" distance between collars when fully open. The top collar on both the 6" and 8" adapters accepts "I.D." Flex Liner and the bottom collar is crimped to fit into most stoves or inserts. The Adapter is made of 24 guage 304 stainless steel. This Adapter attaches with self-tapping screws or rivets. A clean-out door comes standard on the Adapter.