Why so large? Just the way the image was formatted, I suppose.

Why that image? It illustrates the first answer on this thread, from 93mouse, "It is just as a nickel - five-cent coin".

Why is a U.S. five cent coin referred to as a 'nickel'? The original five cent coin, as defined in the Mint Act of 1792, was a silver 'half dime' that was half the weight of the ten cent 'dime' and of the same alloy.

In the 1860s, with the Civil War raging and people hoarding all silver and gold coinage (which was also being shipped abroad by speculators as metal prices rose), there was a severe shortage of 'small change' in the United States.

In desperation, the public resorted to use of postage stamps as currency which became a great nuisance as they brought ragged, used, stamps to post offices to exchange for new ones.

As remedy, the Treasury Department issued 'Fractional Currency' notes of three to fifty cents as well as 'base metal' low denomination coins. Along with changing the cent composition to bronze in 1864 a new two cent bronze coin was added and in 1865 the three cent silver (1851 - 72) was joined by a three cent coin with a new composition of 75% copper, 25% nickel - the first 'Nickel'.

With the success of the new three cent 'nickel', a new five cent coin of the same 75/25 copper nickel mix was introduced in 1866, though the silver half dime would also be produced in decreasing numbers through 1873. The three cent 'nickel' was produced only through 1889, then largely forgotten. Over time the five cent became known as a 'Nickel' and is produced in the same metal today.

First U.S. 'Nickel' - Three Cents

Second 'Nickel' - Five Cents

Fractional Currency

By 1889 the emergency had passed, metal prices normalized, the two cent and three cent coins had been eliminated, but the one cent bronze and five cent 'nickel remained in production.

Why did the 1913 - 1938 'nickel' portray a Native American and a bison? In the early 20th Century, President Theodore Roosevelt had decided that U.S. coinage designs then in use were just plain bland. He sought artists from outside of the mint to design coinage that would 'reflect the American spirit' and for the five cent coin engaged the eminent husband and wife sculptors James and Laura Fraser. Fraser was well known as an artist and sculptor and would create the well known 'end of the trail' statue that was displayed at the 1915 Pan Pacific Exposition at San Francisco.

End of the Trail - James Fraser

The original plaster sculpture was subsequently displayed for decades at Mooney Park in Visalia, California (just 'down the hill' from where I now sit) until it was 'swapped' in 1968 to the National Cowboy and Western Heritage Museum in Oklahoma City, OK, in exchange for an exact cast bronze replica which is now at Mooney Park.

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Why is the name of a German riflescope pronounced the same as the word for a U.S. five cent coin? Beats me... I'm not a linguist.