Green’s Dictionary of Slang

(UK Und.) one who operates a game of thimble-rig n.

1732		Derby Mercury 28 Sept. 3/1: A Parcel of thimble-men [...] decoyed him out of about 10l.
1830		Egan Finish to the Adventures of Tom and Jerry (1889) 166: It is not the intention of the ‘thimble-coves,’ under any circumstances, to lose.