Fey, Mills, And The Operator Bell
In 1907, it is reported that Charles Fey collaborated with the Mills Novelty Company to produce the Mills Liberty Bell, which represented an advance in terms of the mass manufacturing and distribution of the machine. He never sold the actual rights to the manufacturing of the machine, but it simply was not possible to obtain a patent to protect the design of a gaming device. In 1910, the Mills company devised another slot machine - the "Operator Bell," which brought with it some fundamental differences in the way the game was played and how it paid out.
For one thing, the machines had the now-familiar "goose neck" through which the coins would be entered into the machine. More importantly, the Operator Bell doubled the number of symbols that were on each reel, from the ten that were on Fey's original machine to twenty.
When the number of symbols on each reel increased to 20, that increased the number of possible combinations that could be made to a figure that was now 8000. Naturally, that served to increase the potential jackpot payoff to the player as well.
The Operator Bell was also significant for yet another reason, which contributed to its cachet in popular culture - it was the first slot machine that used fruit for symbols. This is obviously a custom that continues to this day. In fact, fruit symbols have become so identified with the slot machine that in the United Kingdom the devices are commonly known as "fruit machines."
With over 30,000 of them manufactured, the Operator Bell slot machine was the dominant gaming device of its era, and opened the door for the continued advancement in technology that would lead to it becoming a mainstream part of Americana.