What are the meta/viny furance/main-duct connectors called?

Thanks again for your help about bricks under the furnace.
What do you call those things in the main ductwork close to the furnace that are mostly vinyl, 6 inches high, that clamp on to the ducts at each end?
There's a band about an inch wide at each end. One end clamps on a short duct from the furnace, and the other end clamps on the outgoing or incoming duct from the house.
In the middle of that is a piece of grey vinyl about 4 inches wide, following the perimeter of the duct it's attached to.
I need to replace mine but I don't know what they are called.
Do you know if they are there to keep vibration noise from getting into the ducts, or to make up for minor misalignment between the furnace and the duct?
Thanks.
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Never having seen one I would guess for vibration noise from getting into the ducts, or to make up for minor misalignment between the furnace and the duct.
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Yes - to both misalignment and noise control.

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