Why do some coins have ridged edges?

Ridges, also called reeding or serrations, were introduced to protect coins made of precious metal. A coin with a grooved edge shows at once if someone has shaved metal from it, and it is harder to copy. On modern coins made of cheap metal the ridges no longer protect anything, so they persist mainly out of habit and familiarity. [1] [2]

Early coins were hammered by hand, and the metal spread out under the blows, so they had no uniform edge. Because a coin's value was tied to its weight in gold or silver, people could file or shave off a little metal and keep the shavings. This is called clipping. According to the Perth Mint, heavy coins tended to be hoarded, which left clipped coins in circulation, a pattern known as Gresham's law. Clippings were also sometimes mixed with base metals to make counterfeits, and even severe punishments, including death, did not stop the practice. [3]

Mints tried other remedies first. NGC notes that medieval coins were thin and had no room for an edge design, so die cutters sometimes added dots or denticles around the border as a warning if metal had been removed. Many coins were struck off-center, so these borders were often missing anyway, and clipping stayed common for centuries. [2]

A clipper could trim a little from each of many coins, collect the shavings, and still spend the coins as if they were unaltered. A reeded edge ruined this scheme because a shaved edge was immediately obvious. [4]

The screw press, adopted by nearly all western mints in the 16th and 17th centuries, produced more uniform, better-centered coins. Thick gold and silver coins could be given edge lettering, such as the Latin phrase DECUS ET TUTAMEN used on British coins, while thinner coins received reeded edges. The collar, a hardened ring that surrounds the blank during striking, also stopped metal flowing outward. Jean-Pierre Droz, a Swiss-born engineer, is said to be the first to see that the collar could work as a third die, carrying lettering or a pattern onto the edge. Littleton Coin says reeding came into widespread use with collar dies in automatic presses in the late 1700s and 1800s. [2] [3] [1]

Counterfeiting became harder as a side effect, since a forger now had to reproduce a third pattern on the edge as well as the two faces. [1]

The US Mint dropped edge devices from base-metal minor coins after 1795 because they were not worth clipping, which is why pennies and nickels are smooth. Dimes, quarters and halves kept reeding even after the Coinage Act of 1965 removed their silver. NGC says the reeding now serves no useful purpose and survives for familiarity and tradition. Mental Floss adds that the government reused the existing dies and collars rather than pay for new ones. [2] [4]

Sources also mention a practical benefit: ridges, whether continuous or interrupted, are said to help blind and visually impaired people tell denominations apart by touch. They also give coins a more finished look. [3] [4] [1]