The author remixed this model.
Added a larger top with room for a band clamp and a taper. The taper could be reduced, but my need was for an air return flex duct that is of questionable “6-inch” diameter.
Side note - this is the second attempt - the interior diameter of the original was 6 inches or thereabouts, if you want to just extrude the original for more collar, a six-inch crimp will fit inside that diameter. The final picture (with the wye) is an example of my first happy accident.