Why do coins have ridges on their edges?

Those tiny grooves are a 300-year-old security system. When coins were struck from real silver and gold, the metal in your pocket was worth exactly what the coin said — which made every smooth edge an invitation. Thieves would shave a thin sliver off the rim, spend the coin at face value, and melt the shavings into profit. Do it to enough coins and you're quietly minting money. The fix was mechanical, not moral: cut a fine pattern of ridges — reeding, the mint's word for those machined grooves — into the edge. Now any shaved coin betrays itself instantly, because the pattern is broken where the blade passed.

The clipping economy

Edge-shaving, called clipping, was rampant in 17th-century England. By the end of that century, nearly half the silver content had vanished from the coins in circulation. The crown's response was to machine ridged edges onto new coinage, turning every coin into its own tamper seal. When the United States set up its own mint in 1792, it adopted reeded edges for silver and gold coins from the start.

Why some coins stayed smooth

Look at a penny or a nickel: smooth all the way around. Neither ever carried enough precious metal to be worth shaving, so they never needed the defense. Dimes, quarters, and half dollars — all once struck in 90% silver — got the ridges. A US quarter carries 119 of them; a dime carries 118.

The silver left. The ridges stayed.

In 1965, Congress pulled silver out of dimes and quarters and replaced it with a copper-nickel sandwich. The original threat was gone, but the ridges survived because they picked up new jobs: they make coins harder to counterfeit convincingly, and they let anyone — including blind and low-vision users — tell a dime from a penny by touch alone. A theft deterrent quietly became an accessibility feature.