What classification does a letter that is square instead of rectangular fall under?

The correct classification for a letter that is square instead of rectangular is nonmachinable. This is because most postal sorting and processing machines are designed to handle rectangular letters efficiently, adhering to standard size requirements. When an item is square, it does not conform to the typical dimensions that these machines are built to process.

Nonmachinable items often require manual handling, which can lead to additional costs and longer processing times. This classification helps postal services determine the appropriate rates and handling procedures for different types of mail based on their size and shape.

Other classifications, while relevant in different contexts, do not apply in this case. For example, machinable refers to items that fit within the standard dimensions that postal machines can efficiently process. Oversized refers to mail that exceeds standard dimensions, which typically applies to larger rectangular items, not square letters. Standard usually denotes letters that meet the typical size and weight requirements for machine processing, which square letters do not fit into.