Under 15 USC 1242 (the Switchblade Knife Act), it is illegal to introduce into interstate commerce any switchblade knife. If you were to do so, you would be subject to a $2,000 fine and up to five years in prison. The knives themselves are subject to forfeiture. There are certain exceptions for the carrier and for knives for the Armed Forces. It is also legal for a person with one arm to carry on his or her person a switchblade with a blade three inches or less in length. Finally, there is a complicated exception for spring action knives that have a mechanical bias toward being closed and require exertion of the hand, wrist, or arm to overcome that bias (sort of a reverse switchblade).
Customs' regulations define a switchblade as:
Any imported knife, or components thereof, or any class of imported knife, including "switchblade," "Balidong," "butterfly," "gravity" or "ballistic" knives, which has one or more of the following characteristics or identities:
(1) A blade which opens automatically by hand pressure applied to a button or device in the handles of the knife, or any knife with a blade that opens automatically by operation of inertia, gravity, or both . . . .
Occasionally, a prospective knife importer is smart enough to know about this law. Even more occasionally, that importer will ask Customs for a ruling on whether a particular knife is a banned switchblade. Such is the case in HQ H229916 (Nov. 12, 2012).
The knife at issue in the ruling is described as an "Out the Front" knife. It is 8" overall, with its 3" blade extended. As you might gather from the name, the blade slides straight out of the handle. Here is a picture Customs included in the ruling:
Not surprisingly, CBP determined that this knife falls within the definition of switchblade in its regulations. Consequently, it is inadmissible. So, whether you are a Shark or a Jet, if Customs Officer Krupke sees your container of Out the Front knives, you are going to lose them.