This custom-made light gray plastic mailing container also doubles as a protective holder for the cartridges (used by the National Library Service's digital talking book player, and American Printing House for the Blind's Book Port DT and Joy Player. Each postage-free container comes with the imprint: “A Free Matter for the Blind or Handicapped” and holds a single cartridge that can be used to safely send cartridges through the mail. You can also use this container to keep your cartridges safe and clean. Cartridge not included.