I must not understand the categories then. I was of the understanding that media mail is 3rd class, unless the weight is over 16oz (I messed up above and put 13oz), at which time it becomes 4th class media mail. There is a library rate, which is cheaper, but it has to be between libraries. And there's the bound printed matter category. I send my books media mail, because they do open packages nowadays, as periodic audits. Please, correct me if I'm wrong. If there is a cheaper way, I'd love to use it. I mail a lot of books.