When I'd go to antique shows/flea markets, I'd see these Wizard (and other brands) of "card holdout" cheating devices all the time, at least they were advertised by the dealers as such. They also appear on eBay frequently. I even own a few. They are about 2" long. Never saw this display of them before, so I thought I'd show it here.

They are not really made for cheating, are they? What exactly was a "cuff holder" needed for?

Robert

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Akim Tamiroff in "King of Gamblers" (1937).
"A fast moving and low budget crime drama seasoned with mystery & comedy. ... Akim Tamiroff, Paramount's resident crime lord, runs all the illegal gambling activities in a major city. Reporter Lloyd Nolan struggles to get the goods on Tamiroff, but runs up against a stone wall until he meets sexy but tough nightclub singer Claire Trevor (obviously dubbed). Trevor is anxious to avenge the death of her innocent sister (Helen Burgess), who was done in by Tamiroff's henchmen. ... Based on the FBIs J. Edgar Hoover book Persons in Hiding.," per IMDb.
http://www.antiquegamblingchips.com/StillsB_OtherMaleActors.htm