Green’s Dictionary of Slang

(Aus./US) a knuckleduster.

1915		Bulletin (Sydney) 2 Sept. 26/1: The night afore last one of the guns from the den up the alley whooshed me a bonzer on the mush with a duster.
1935		Thieves Slang ms list from District Police Training Centre, Ryton-on-Dunsmore, Warwicks 4: Duster: Knuckleduster.
1940		J. Archibald ‘No Place Like Homicide’ in Popular Detective Apr. 🌐 They had tapped the currency carrier over the noodle with a hard object [...] The criminal character who handled the duster had been just a little too energetic.
1961		(con. c.1950) R. Poole London E1 (2012) 340: Feeling the weight of the ’dusters in his pockets.
2011		R. Goodwin ‘Threshold Woman’ in Pulp Ink [ebook] He carries a pair of dusters with him [...] and he collects the teeth of his victims.