Product review (5 stars): 3 inch to 4 inch exhaust duct expander
This worked fine in my exhaust duct application for a 5 kilowatt electric generator that I installed in my basement. It's muffler terminated in a 3 inch round pipe and this adapter increased it to 4 inches, so that I could then use a standard 4 inch colapseable-expandable dryer vent duct to route the exhaust out of an exterior wall.