A letter-size piece is nonmachinable if it has one or more of the following characteristics (see new DMM C010.1.1) for how to determine the length, height, top, bottom, and sides of a mailpiece):

1. If the aspect ratio (length divided by height) is less than 1.3 or more than 2.5.
2. If it is polybagged, polywrapped, or enclosed in any plastic material.
3. If it has clasps, strings, buttons, or similar closure devices.
4. If it contains items such as pens, pencils, or loose keys or coins that cause the thickness of the mailpiece to be uneven.
5. If it is too rigid (does not bend easily when subjected to a transport belt tension of 40 pounds around an 11-inch diameter turn).
6. If it is a mailpiece more than 4-1/4 inches high or 6 inches long and the thickness is less than 0.009 inch.
7. If is is a First Class piece weighing 1-ounce or less and having a nonmachinable characteristic subject to the 1-ounce letter rate .41 plus .17 surcharge.
8. If it is a First Class letter weighing less than 1-ounce and having a nonmachinable characteristic subject to the applicable additional ounce rate.
9. If it weighs more than 3.5 ounces
10. If it is a booklet with the bound edge (spine) along the top of the piece (length) or along the shorter dimension and is not secured (tabbed).