I don't think so from what the post master was telling me basically if you can get it to fit they ship it ...... I shipped some stuff a while back and he was telling me about that in case I shipped some motor parts ( local guy real cool about that shit ) ..... hence FLAT RATE BOX LMAO
off their site : Introducing a quick, easy, and convenient way for you to ship Priority Mail packages. The Priority Mail Medium Flat Rate Box features predetermined rates regardless of weight (domestically) or destination, similar to the Flat Rate Envelope.