Downspout to plastic pipe adapter

I needed an adapter to transition from a 4" X 3" downspout to a 3" plastic pipe that carries rainwater away from the house. The one supplied by the contractor that installed the downspout was too restrictive and constantly plugged if anything larger than a small twig was washed down the downspout. The last time it plugged up, I decided to design a much more free flowing transition adapter, and here it is.
The holes for joining the two halves are for 1/4" bolts and nuts..