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Publication 52 - Hazardous, Restricted, and Perishable Mail >
Appendix C > USPS Packaging Instruction 9B
A magnetized material is an article that has a magnetic field strength capable of causing the deviation of aircraft instruments. Magnetized materials include magnets and magnetized devices such as magnetrons and light meters of sufficient strength to possibly cause erroneous aircraft magnetic compass readings. Magnetized materials are mailable, provided that all requirements in 349.24 are met.