Product review (5 stars): Important - you MUST buy the Broan DC4 4" Duct Collar if you are using flexible ducting.
One thing that reviewer R.Fisk and reviewer ViennaPMS found out is that for any sort of flexible ducting to be used with this product you MUST also have the Broan DC4 4" Duct Collar. Nothing else will work! There is absolutely no way to attach the flexible ducting to this product without the duct collar. Something that product information or product specification fails to mention.
So like ViennaPMS says just buy the Broan kit. Had to order the duct collar after I got my vent cap.
Give the product 5 stars for quality - not taking any points off for not making clear that the duct collar is needed for flexible ducting.