In my area we seem to have three seasons, snow, rain, and stupid birds that can build a fifty pound nest overnight, I wanted to replace my plastic cup with a flapper. I always forget to put the cup back. I could have just went to my parts supplier and bought one but I have more fun when I build things myself. I dug some different thickness of bar stock out of my scrap pile and in a couple of hours had a working flapper. It is not fancy but keeps the birds out, also it's easier to send smoke signal now too.
Pete.