I've noticed downspout tubing sold at my local big box stores (HD, Lowes) are a rectangular size, not sure exactly what.
The stuff on my house is square (with rounded corners of course), maybe 2.5 inches per edge.
Is this some standard size? I cannot seem to find information on it on the net. I expect all the houses built by my builder in this subdivision to use this same downspout size.
(A favorite retailer of mine sells accessories that work with 2x3 and 3x4 inch downspouts, but alas, these are all non-fitting for my home.)