Just do a quick search, here are some examples. I know if you look at the amended AB1237 that is crossed out, but the definition still fits the one used and the same definition can be found in multiple bills.
From AB1237 "(7) As used in this section, "metal knuckles" means any device or instrument made wholly or partially of metal which is worn for
purposes of offense or defense in or on the hand and which either
protects the wearer's hand while striking a blow or increases the
force of impact from the blow or injury to the individual receiving
the blow. The metal contained in the device may help support the hand
or fist, provide a shield to protect it, or consist of projections
or studs which would contact the individual receiving a blow."
Many bills use this type of language, refering to "metal knuckles" as a "deadly weapon" and imposing minimum penalties for possession, etc.
From SB194 "For purposes of this subdivision, "deadly weapon" is defined to include any instrument or weapon of the kind commonly known as a blackjack, slungshot, billy, sandclub, sandbag, metal knuckles, any dirk, dagger, pistol, revolver, or any other firearm, any knife having a blade longer than five inches, any razor with an unguarded blade and any metal pipe or bar used or intended to be used as a club."
If you go to the site for your state, many states have a search engine where you can search all bills, just do a search for "metal knuckles" to see what the laws in your state are. For example:
(720 ILCS 5/24-1) Sec. 24-1. Unlawful Use of Weapons.
(a) A person commits the offense of unlawful use of weapons when he knowingly:
(1) Sells, manufactures, purchases, possesses or carries any bludgeon,black-jack,slung-shot,sand-club, sand-bag, metal knuckles, throwing star, or any knife, commonly referred to as a switchblade knife, which has a blade that opens automatically by hand pressure applied to a button, spring or other device in the handle of the knife, or a ballistic knife, which is a device that propels a knifelike blade as a projectile by means of a coil spring, elastic material or compressed gas; or...
