Metal feeders aren't the whole solution, though. I had one, hanging on a tree branch. The squirrels jumped up and down on the branch until the feeder fell to the ground and the top came off!
I now have a 'Squirrel Buster' feeder. It has a mechanism whereby if the weight is too much on the perches, it closed over the seed holes. It works for larger birds, too, like the dang starlings and grackles. Rats with wings, they are.