Here is the MISSouri Code on the issue. Knuckles are not legal and considered a deadly weapon
Possession--manufacture--transport--repair--sale of certain weapons a crime--exceptions--penalties.
571.020. 1. A person commits a crime if such person knowingly possesses, manufactures, transports, repairs, or sells:
(1) An explosive weapon;
(2) An explosive, incendiary or poison substance or material with the purpose to possess, manufacture or sell an explosive weapon;
(3) A machine gun;
(4) A gas gun;
(5) A short barreled rifle or shotgun;
(6) A firearm silencer;
(7) A switchblade knife;
(8) A bullet or projectile which explodes or detonates upon impact because of an independent explosive charge after having been shot from a firearm; or
(9) Knuckles - "Knuckles" means any instrument that consists of finger rings or guards made of a hard substance that is designed or adapted for the purpose of inflicting serious physical injury or death by striking a person with a fist enclosed in the knuckles
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