Here are some tips:
Check out what it’s made of. Carry a refrigerator magnet and if it sticks to the machine, it’s iron, and it’s old!

Clockwork mechanisms are 1880s to 1890s. Bronze mechanism parts are usually 1895 through 1905. Castings in the mechanical parts are up to 1919, with stamped steel mechanism parts are 1920s or thereafter. Nickel plating is circa 1897-1922, when chrome plating came in and stayed.

Crackle finish is late 1920s through mid-1930s. Smooth non-chipped paint is post WWII, likely 1950s or later. Formica cabinets are after 1960.

There are some generalizations that apply to slot machines, pinballs and arcade machines. Cast iron was in general use up until the early 1920’s when it was replaced with aluminum. The electro- mechanical age began for pin games and arcade machines in the mid 1930′, but it was not implemented with slot machines until 1964 .

Refer to early trade magazines, catalog reprints and current publications (reputable books specializing in specific collectibles). The latter best serves the majority of collectors as they are readily available.

One way is by the patent number. For example, the patent number 1,743,000 was issued in 1930. Therefore, if you machine bares that number, you know that your machine was made after 1930.

Here are some key patent numbers. The first patent number was issued in 1836. Number 650,000 – issued in 1900. Number 1,350,000 in 1920, and Number 2,200,000 in 1940.

The patent date, however, can be very misleading because sometimes a patent on a specific part of the machine was patented many years before the machine itself was manufactured.

It’s a lot like being a private investigator!!