Usps flat rate boxes

I like this one, I have shipped slant 6 intakes and exhaust (separately) and small block intakes in it....

If you can't find the size that you need, you can order them online from the post office and they will send you a bundle free... If you don't need a whole bundle, just take what you need and bring the rest to your local post office...

I have found that some post offices do not carry all the available sizes, so look around or order them online...