Dave the pilum knife is the Russian model that actually shoots the blade out of the knife like a spear gun. They are illegal in all of the USA and are very poorly made garbage. This is the only knife I agree with being banned every where.
Levine's link is helpful, but the real sense of the law lives in the court system and local police as to how it is enforced. In NYC the present day view is all knives are bad, and in other parts of NY the enforcement seems to be different. In NYC, if you can hold the blade and flick the handle open it is considered a gravity knife !! This has held up in court and remember this is the state law that is being enforced there. I have been out of law enforcement in NYC for years now, but in my day there were never an arrest for simple knife possession. It is considered a good collar now.....times have changed for the worse....