Federal Switchblade Act as Amended by Congress and signed into law by President Obama on October 28, 2009. The amendment added exception (5), shown in red below, which specifically allows for one-hand opening and assisted opening knives:
Section 1241. Definitions
As used in this chapter –
(a) The term “interstate commerce” means commerce between any State, Territory, possession of the United States, or the District of Columbia, and any place outside thereof.
(b) The term “switchblade knife” means any knife having a blade which opens automatically – (1) by hand pressure applied to a button or other device in the handle of the knife, or (2) by operation of inertia, gravity, or both.
Section 1242. Introduction, manufacture for introduction, transportation or distribution in interstate commerce; penalty
Whoever knowingly introduces, or manufactures for introduction, into interstate commerce, or transports or distributes in interstate commerce, any switchblade knife, shall be fined not more than $2,000 or imprisoned not more than five years, or both.
Section 1243. Manufacture, sale, or possession within specific jurisdictions; penalty
Whoever, within any Territory or possession of the United States, within Indian country (as defined in section 1151 of title 18), or within the special maritime and territorial jurisdiction of the United States (as defined in section 7 of title 18), manufactures, sells, or possesses any switchblade knife, shall be fined not more than $2,000 or imprisoned not more than five years, or both.
Section 1244. Exceptions
Sections 1242 and 1243 of this title shall not apply to –
(1) any common carrier or contract carrier, with respect to any switchblade knife shipped, transported, or delivered for shipment in interstate commerce in the ordinary course of business;
(2) the manufacture, sale, transportation, distribution, possession, or introduction into interstate commerce, of switchblade knives pursuant to contract with the Armed Forces;
(3) the Armed Forces or any member or employee thereof acting in the performance of his duty;
(4) the possession, and transportation upon his person, of any switchblade knife with a blade three inches or less in length by any individual who has only one arm; or
(5) a knife that contains a spring, detent, or other mechanism designed to create a bias toward closure of the blade and that requires exertion applied to the blade by hand, wrist or arm to overcome the bias toward closure to assist in opening the knife.
Further references to Switchblades in U.S. Code found at:
Title 18 – Crimes and Criminal Procedure
Part 1 – Crimes Chapter 83 – Postal Service
Section 1716. Injurious articles as nonmailable
(g) All knives having a blade which opens automatically (1) by hand pressure applied to a button or other device in the handle of the knife, or (2) by operation of inertia, gravity, or both, are nonmailable and shall not be deposited in or carried by the mails or delivered by any officer or employee of the Postal Service. Such knives may be conveyed in the mails, under such regulations as the Postal Service shall prescribe –
(1) to civilian or Armed Forces supply or procurement officers and employees of the Federal Government ordering, procuring, or purchasing such knives in connection with the activities of the Federal Government;
(2) to supply or procurement officers of the National Guard, the Air National Guard, or militia of a State ordering, procuring, or purchasing such knives in connection with the activities of such organizations;
(3) to supply or procurement officers or employees of any State, or any political subdivision of a State or Territory, ordering, procuring, or purchasing such knives in connection with the activities of such government; and
(4) to manufacturers of such knives or bona fide dealers therein in connection with any shipment made pursuant to an order from any person designated in paragraphs (1), (2), and (3).
The Postal Service may require, as a condition of conveying any such knife in the mails, that any person proposing to mail such knife explain in writing to the satisfaction of the Postal Service that the mailing of such knife will not be in violation of this section.
(h) Any advertising, promotional, or sales matter which solicits or induces the mailing of anything declared nonmailable by this section is likewise nonmailable unless such matter contains wrapping or packaging instructions which are in accord with regulations promulgated by the Postal Service.
(i)(1) Any ballistic knife shall be subject to the same restrictions and penalties provided under subsection (g) for knives described in the first sentence of that subsection. (2) As used in this subsection, the term “ballistic knife” means a knife with a detachable blade that is propelled by a spring-operated mechanism.
(k) For purposes of this section, the term “State” includes a State of the United States, the District of Columbia, and any commonwealth, territory, or possession of the United States.