knuckle duster vs brass knucks

knuckle duster and brass knucks both are nouns.

Word	Noun	Adjective	Verb	Adverb
knuckle duster	Yes	No	No	No
brass knucks	Yes	No	No	No

As nouns, knuckle duster and brass knucks are synonyms defined as:

knuckle duster and brass knucks: (used in the plural) a small metal weapon; worn over the knuckles on the back of the hand

Other synonyms of knuckle duster include brass knuckles, knuckles, knucks.

knuckle duster (noun)	brass knucks (noun)
(used in the plural) a small metal weapon; worn over the knuckles on the back of the hand	(used in the plural) a small metal weapon; worn over the knuckles on the back of the hand