Ever wonder why the governments spends so much money on creating those tiny little ridges along the edges of a coin? Wouldn’t it be easier and cheaper to build a plain one? Of course, it might save some money to make the edges smooth. However, there is a very practical reason for putting this ridges on coins.
The story goes back to 1792 when the Coinage Act declared that gold eagles, half eagles and quarter eagles ($10, $5 and $2.50 coins respectively) would be made of their face value in gold. The dollar, half-dollar, quarter dollar, dime and half-dime coins were to be manufactured of their value in silver. And the cent and half-cent coins were to be made of copper. The edges of these coins were smooth.
Nefarious individuals realized that they could make a reliable profit from these coins if they filed down or shaved down the sides of gold and silver coins and sell them as precious metal–while passing the coins as unaltered. In responses, the U.S. Mint started to put the ridges, also called “reeding”, on the sides of valuable coins. This reeding was a security feature. It impossible to shave along the edges without the tampering being visible. The ridges also conveniently made the coins distinguishable by touch, which helps visually-impaired citizens tell similar-sized coins (like pennies and dimes) apart. Pennies and dimes may be small coins today, but the difference used to be very important back during the Great Depression era.
Of course today, most U.S. coins are not made of precious metals like silver and gold, but U.S. half-dollars, quarters, and dimes still keep with this tradition.