To be classified as a flat size mail piece, what test must it pass?

To be classified as a flat-sized mail piece, the item must primarily pass the flexibility test. This test assesses whether the mail piece can be easily bent or folded without causing damage to its contents or structure. Flat-sized mail pieces have specific criteria and typically must be able to maintain a certain level of flexibility, distinguishing them from other shapes and sizes like letters or packages.

The flexibility of a mail piece is crucial because it affects how it can be processed through automated sorting systems. If a mail piece is too rigid, it may not fit properly through the machines used by postal services, potentially leading to delays or misclassification.

In comparison, while weight, dimensional, and stability tests might be relevant for different types of mail pieces or other classifications, they do not specifically determine if an item can be considered flat-sized. The flexibility test is central to maintaining efficiency and effectiveness in postal operations concerning flat mail.