Publication 52 - Hazardous, Restricted, and Perishable Mail > 4 Restricted Matter > 44 Knives and Sharp Instruments
Sharp instruments include all sharp–pointed or sharp–edged implements such as knives, tools, ice picks, razor blades, stilettos, or similar devices. When uncertain about the mailability of a sharp instrument or a switchblade knife, a ruling may be requested from the local postmaster (see215.3).
A switchblade knife has a blade that opens automatically by hand pressure applied to a button or other device in the handle, or by operation of inertia, gravity, or both.