4" HT Pipe Adapter is constructed by Selkirk. This adapter is used as a vertical or horizontal connection between the single wall 4" chimney pipe length and  Insulated Class A connector pipe.

You have single wall pipe and our 4 inch insulated pipe.  How do you put them together?  That is to say, how do you join the 2 safely?  You use this 4" HT Pipe Adapter by sliding one end into the single wall and the other end you will twist and lock the insulated pipe to.  Most importantly, you should seal it at the single wall side of the connection. The  and extra sections of 4 Inch pipe don't need to be sealed, but they do need to be twisted and locked and screwed together. It will fit into this piece where you seal it. https://flameinnovation.com/product/4-adjustable-roof-flashing-1/

In short, you now have a safe and secure installation. Most importantly you have to pay attention to your layout of your exhaust. For example,  you don't want to put this piece into a single wall exhaust and then make the transition too close to the ceiling.  Furthermore, if you need to, you can cut the single wall down a bit. Use this adapter to keep at least 16" away from your ceiling with single wall pipe.  In a wall tent it doesn't matter, but in a house or RV it does.  The single wall 4" pipe has a clearance to combustibles of 12" around it. Be safe. Think it through. Ask us questions. We are here to help. Always have a carbon monoxide detector on hand. https://www.safewise.com/resources/carbon-monoxide-detectors-guide/