Publication 52, Hazardous, Restricted, and Perishable Mail > Appendix C > USPS Packaging Instruction 1A
The proper shipping name for a mailable toy propellant device is “model rocket motor” or “igniter.” A device that is assigned identification number NA0323 or UN0454 and classed as a Division 1.4S explosive is eligible for mailing in domestic mail via surface transportation only, provided that all requirements are met and the device is properly packaged as follows.
Prior written permission must be obtained from:
Manager, Product Classification USPS Headquarters 475 L’Enfant Plaza SW, Room 4446Washington, DC 20260
Mailable devices must meet each of the following conditions:
Note: Full responsibility rests with the mailer to comply with Bureau of Alcohol, Tobacco, Firearms, and Explosives (BATFE) regulations before mailing. A legible photocopy of the Product Classification Manager‘s approval letter must be presented by the mailer to the Postal Service acceptance clerk at the time of mailing.