19 x 16 square to 6 round transition made from galvanized sheet metalcustom made per your measu.
Sheet metal transition from square to round.
Step 1 use a square or rectangle to round transition calculator.
Larger square to round transitions such as this require many separate bends to produce bending the flat piece of metal so that the square cones into a round is usually done on a 10 ft hand brake that s a lot of effort.
Converting a rectangle to round sheet metal duct work is something that is common in hvac.
These may be with or without duct sealant.
Square to round smc spiral fittings are manufactured with an elbow lock seam lap seam i e.
With some careful planning this is something you can do yourself.