: More than 11-1/2 inches but not more than 15 inches long.
: More than 6-1/8 inches but not more than 12 inches high.
: It is a thermoregulating, mid-weight wool-nylon blend designed as a versatile base layer or next-to-skin piece. 145 Mail Preparation - Postal Explorer - USPS
To qualify under these standards, the pieces must meet specific dimensions:
: Prepared mail must be presented directly to the specific delivery Post Office or destination unit (DDU/S&DC) responsible for those routes.
: All mailpieces must be separated by delivery route or Post Office Box section.
: Delivery statistics and route information must be obtained using the USPS EDDM web tool . Physical Standards for 145 Flats