Most brass knuckles are legal on the federal level, but many states and counties within the United States regulate or ban the manufacture, sale or possession of brass knuckles, reports The Law Dictionary. Internationally, many countries, such as Switzerland, classify brass knuckles as illegal weapons, adds Laws.com.
Kentucky allows the possession of brass knuckles but classifies them as deadly weapons. A permit is required to conceal-carry brass knuckles in Kentucky, notes CriminalDefenseLawyer.com. Other states are more strict in their brass knuckles law. For example, California and Vermont prohibit not only the possession of brass knuckles but also of anything that looks like brass knuckles, such as plastic knuckles, according to FindLaw