Help With Flue Adapter to Hardpipe

[Cajundave10]

I need to connect this: https://chimneylinerdepot.com/shop/reducers-increasers/reducerincreaser-11inf-to-10inf/

To this:

Reducer/Increaser - 11in(F) to 10in(F) - Chimney Liner Depot

Reducer/Increaser - 11in(F) to 10in(F)

chimneylinerdepot.com

The adapter/reducer attaches to a cut off section of my flue that is drilled in with stainless screws.

My question is: The double walled pipe connects to the interior section of the 10” hardpipe. How do I secure the 2 pieces together? Caulk? Longer screws? any help is appreciated.

 

[begreen]

Is this for the outdoor fireplace and is that fireplace set up for air cooled chimney. Subsitutes are not allowed there.

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