You've heard of the National Rifle Association, but have you ever heard of the National Brass Knuckles Association? No, well, there isn't one. That may have something to do with why most states outlaw possession of brass knuckles.
TL;DR (Too Long; Didn't Read)
Brass knuckles are illegal in many states, but the laws about exactly what is illegal are different. Some states make all knuckle weapons illegal, regardless of what they are made of, while others have different laws for concealed and open-carry brass knuckles.
Life and Times of Brass Knuckles
Brass knuckles is the colloquial term for a hand weapon made of a solid material with holes in it for four fingers. It often looks like a line of connected finger rings, both protecting the fingers when you punch and delivering a damaging blow. Brass knuckles can break bones or burst blood vessels.
This weapon has been around since the time of the Romans, when the concept was incorporated into the Roman hand guard or glove, called the caestus. During World Wars I and II, American soldiers carried the Mark I Trench Knife equipped with brass knuckles.
Today, brass knuckles are used by street fighters, either on one or both hands, and remain very dangerous weapons. In many states, they are illegal, but the details of the laws vary.
Laws about Brass Knuckles
Federal law does not regulate brass knuckles, but state and city laws do, and the laws are all over the map. Brass knuckles, often simply called "knuckles" in state statutes, are prohibited outright in many states. Some states, including California, Michigan, Illinois and Vermont, prohibit doing almost anything with brass knuckles or look-alikes made of other materials. They make it illegal to own, possess, sell or use brass knuckles.
Some states outlaw knuckles made of brass but not those constructed of other hard substances, including plastic. Still other states, like South Carolina, make it illegal to possess brass knuckles only if you have an "intent to commit a crime." If you don't intend to commit a crime, you can own brass knuckles and carry them without any type of permit. Georgia law defines brass knuckles as a weapon only if someone brings them onto school property or at school functions. On the other hand, Georgia bans concealed weapons, including brass knuckles. Similarly, under Florida law, you can be charged with possessing a concealed weapon if you carry brass knuckles in your pocket or backpack. It doesn't matter if you use the knuckles or plan to use them.