Why did the US make half dimes?

Why a half-dime?This seemingly strange denomination dates from the early 1790s when US coinage was intended to be based on multiples of 10 rather than 100. Proposed denominations were:

• Mill (or mil): Never issued, but still used in tax calculations as a "virtual" denomination.
• Cent: 1 cent = 10 mills.
• Dime: 1 dime = 10 cents
• Dollar: 1 dollar = 10 dimes
• Eagle: 1 eagle = 10 dollars
• Union: 1 union = 10 eagles (never issued)

Each denomination was also split in half with half-cents, half-dimes, half-dollars, half-eagles, and half-unions*. There was also the familiar quarter, but that non-standard denomination was created for compatibility with Spanish coins that were also in used at the time.

In view of that arrangement, a half-dime made sense. But by the 1860s most people were comfortable thinking only in dollars and cents, so the new nickel coin that we still have today was introduced in 1866 and the half-dime was discontinued a few years later.

(*) Half-unions were only struck for a few years, and only as commemorative coins.