Gaffed Pocket Roulette Wheel
This is a picture of an antique gaffed pocket roulette wheel, that used to be sold by the KC Card Co. The operator would place the cover on top, spin the wheel and drop the ball through the hole at the side of the cover. Once the wheel stopped spinning the cover is removed to reveal the result. However, the gaff enables the operator to control if the ball should fall on a red or a black number.
The gaff works on a very simple mechanical principle. Without revealing all the details of the secret, the wheel is made in such way to enable the operator to spin the wheel so that the slots where the ball lands change alignment relative to the numbered divisions. Every other slot is made smaller, so that the ball cannot land into those slots. The numbers alternate between red and black, so by changing the alignment of the rotor the crooked operator can disable either black or red numbers.
This item is very rare and highly collectible. In fact, it is so rare that many reproductions have been made, so be careful if you ever have the chance to buy one of those gaffs.
Below is a clipping from an old HC Evans Blue Book, crooked gambling catalog, showing a listing for the exact pocket roulette wheel pictured above.