4 in. x 4.5 in. Plastic Dryer Duct connector
I used this quick connector as it had a flange that helped cover the oversized hole created for a 4" vent line. The coupler fit right into a 4" aluminum vent line to the exterior. After filling the gap I used HVAC aluminum tape to connect the flange to the concrete wall as there wasn't anyway to connect with screws.
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