Looking to adapt your 2x3 downpipe to mate with the larger 3x4 gutter downspout? The Aquabarrel Downspout to Downspout Adapter is what you need to use.
The injected molded cap will slide over the 3x4 opening and provide you with a rectangular opening to fit your 2x3 downspout pipe. You MAY need to crimp your 2x3 downpipe a bit to make it fit. Not all downspout pipe is exactly the same size/shape. It's easy to crimp the aluminum downspout with a needle nose pliers.
Available in Brown - White