This is a roof drain screen to keep large debris out of downspouts.
Our flat roof has several 1.5 inch openings around the edge which let rainwater drain off the roof. If these openings get clogged with leaves or other large debris, we end up with a miniature lake above our heads. None of the commercial drain screens fit or work well, so I designed this to protect our roof.
Note that I haven't tested these drains on the roof yet; check back in a couple weeks to hear if they work. No warranty given that these will actually protect your roof. Caveat downloader.
More details at makerbot216.blogspot.com/2010/02/making-practical-things.html