In some U.S. states it is illegal to possess and/or carry such a knife in public. In certain jurisdictions, butterfly knives are categorized as a "gravity knife", "switchblade", or "dagger" although they are also occasionally outlawed by name ("butterfly knife").
The knife is illegal in California if blade length exceeds two inches.
In New York, the butterfly knife has been determined to not be a gravity knife.
In Pennsylvania, the butterfly knife is legal for conceal and open carrying.
Butterfly knife trainers feature a special blunt and unsharpened "blade," and are legal in areas where butterfly knives are not.
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for all about them in the US. and if anyone has time. I currently have an open question about knives as well.. if anyone has the time to answer my question I would greatly appreciate it!!!!
the link to my question is::