The weight does not really help because it is the thickness of the product that is the issue since first class mail is only for paper products and keychains shouldn't go through it. None of this really applies to my issue. 

I want to offer both flat stickers and bulky things like keychains and plushies. I want to offer first class mail for orders that include only stickers for cheaper shipping. However, bulky items like keychains wont go through first class mail. I was ...