Here are all the references I could find in NJ law that refers to a knife. The only time blade length is mentioned is when it speaks of selling to a minor.
2C:39-3. Prohibited Weapons and Devices.
e.Certain weapons. Any person who knowingly has in his possession any gravity knife, switchblade knife, dagger, dirk, stiletto, billy, blackjack, metal knuckle, sandclub, slingshot, cestus or similar leather band studded with metal filings or razor blades imbedded in wood, ballistic knife, without any explainable lawful purpose, is guilty of a crime of the fourth degree.
g.Exceptions. (1) Nothing in subsection a., b., c., d., e., f., j. or k. of this section shall apply to any member of the Armed Forces of the United States or the National Guard, or except as otherwise provided, to any law enforcement officer while actually on duty or traveling to or from an authorized place of duty, provided that his possession of the prohibited weapon or device has been duly authorized under the applicable laws, regulations or military or law enforcement orders. Nothing in subsection h. of this section shall apply to any law enforcement officer who is exempted from the provisions of that subsection by the Attorney General. Nothing in this section shall apply to the possession of any weapon or device by a law enforcement officer who has confiscated, seized or otherwise taken possession of said weapon or device as evidence of the commission of a crime or because he believed it to be possessed illegally by the person from whom it was taken, provided that said law enforcement officer promptly notifies his superiors of his possession of such prohibited weapon or device.
2C:39-4. Possession of weapons for unlawful purposes
d. Other weapons. Any person who has in his possession any weapon, except a firearm, with a purpose to use it unlawfully against the person or property of another is guilty of a crime of the third degree.
2C:39-9.1. Sale of weapon to minor; crime of the fourth degree; exceptions
A person who sells any hunting, fishing, combat or survival knife having a blade length of five inches or more or an overall length of 10 inches or more to a person under 18 years of age commits a crime of the fourth degree; except that the establishment by a preponderance of the evidence of all of the following facts by a person making the sale shall constitute an affirmative defense to any prosecution therefor: a. that the purchaser falsely represented his age by producing a driver's license bearing a photograph of the licensee, or by producing a photographic identification card issued pursuant to section 1 of P.L. 1968, c. 313 (C. 33:1-81.2) or by producing a similar card purporting to be a valid identification card indicating that he was 18 years of age or older, and b. that the appearance of the purchaser was such that an ordinary prudent person would believe him to be 18 years of age or older, and c. that the sale was made in good faith relying upon the indicators of age listed in a. and b. above.
2C:39-6. Exemptions
(2)A person carrying a firearm or knife in the woods or fields or upon the waters of this State for the purpose of hunting, target practice or fishing, provided that the firearm or knife is legal and appropriate for hunting or fishing purposes in this State and he has in his possession a valid hunting license, or, with respect to fresh water fishing, a valid fishing license;
(3)A person transporting any firearm or knife while traveling:
(a)Directly to or from any place for the purpose of hunting or fishing, provided the person has in his possession a valid hunting or fishing license; or
(b)Directly to or from any target range, or other authorized place for the purpose of practice, match, target, trap or skeet shooting exhibitions, provided in all cases that during the course of the travel all firearms are carried in the manner specified in subsection g. of this section and the person has complied with all the provisions and requirements of Title 23 of the Revised Statutes and any amendments thereto and all rules and regulations promulgated thereunder; or
(c)In the case of a firearm, directly to or from any exhibition or display of firearms which is sponsored by any law enforcement agency, any rifle or pistol club, or any firearms collectors club, for the purpose of displaying the firearms to the public or to the members of the organization or club, provided, however, that not less than 30 days prior to the exhibition or display, notice of the exhibition or display shall be given to the Superintendent of the State Police by the sponsoring organization or club, and the sponsor has complied with such reasonable safety regulations as the superintendent may promulgate. Any firearms transported pursuant to this section shall be transported in the manner specified in subsection g. of this section;
(4)A person from keeping or carrying about a private or commercial aircraft or any boat, or from transporting to or from such vessel for the purpose of installation or repair a visual distress signalling device approved by the United States Coast Guard.
