United States Postal Service (see Flat-Rate Priority) United States Postal Service (see Flat-Rate Priority) Zone rate USPS Priority Priority Shipping more info Priority Learn about USPS Flat Rate Shipping USPS Priority priority shipping Learn about USPS Flat Rate Shipping (see Flat-Rate Priority) (see Flat-Rate Priority) Learn about USPS Flat Rate Shipping (see Flat-Rate Priority) usps.com USPS Flat Rate Box program