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Publication 52 - Hazardous, Restricted, and Perishable Mail >
4 Restricted Matter > 44 Knives and Sharp Instruments > 443 Packaging and Marking
All sharp-pointed or sharp-edged instruments such as knives, tools, ice picks, razor blades, etc., that are otherwise mailable, must be securely packaged in a strong container. An inner and outer packaging container is recommended. Sufficient cushioning material must be used to protect the sharp points and edges from cutting through the outer packaging during normal Postal Service handling.
No marking of any kind that indicates the nature of the contents may be placed on the outside of any mailpiece containing a switchblade knife.