Why do ridges have coins

Overview

The ridges on coins, technically called reeding, have a history dating back to the late 18th century when coins contained precious metals like silver and gold. The practice began in the United States following the Coinage Act of 1792, which established the U.S. Mint and authorized specific coin designs. Before reeding, coins had smooth edges, making them vulnerable to "coin clipping" - a practice where people would shave small amounts of precious metal from coin edges, then pass the lighter coins at full value while keeping the shavings. This was particularly problematic when coins had intrinsic value based on their metal content. The first U.S. coins with reeded edges were silver dollars minted in 1794, followed by other denominations. Other countries adopted similar edge treatments, with the United Kingdom introducing milled edges on coins as early as the 1660s during the reign of Charles II to combat counterfeiting.

How It Works

Coin reeding works through both mechanical and visual mechanisms. The ridges are created during the minting process when blank metal discs (planchets) are struck between two dies under immense pressure - typically 35-150 tons for modern coins. The collar die that surrounds the coin during striking contains the negative impression of the edge pattern, which is transferred to the coin's edge. For security purposes, the specific number and pattern of ridges varies by denomination and country, making counterfeiting more difficult. Modern coin-operated machines use optical sensors to detect these edge patterns, rejecting coins that don't match expected specifications. The ridges also provide tactile differentiation - visually impaired individuals can distinguish between coins by feeling the edge patterns. Some coins feature interrupted reeding (alternating smooth and reeded sections) or lettered edges for additional security features.

Why It Matters

Coin ridges matter for three primary reasons: security, accessibility, and functionality. Security-wise, reeding prevents both historical coin clipping and modern counterfeiting attempts, protecting the integrity of currency systems. For accessibility, the tactile ridges help approximately 285 million visually impaired people worldwide distinguish between coin denominations without needing to see them. Functionally, coin-operated machines - which process billions of coins annually in vending, parking, and gaming applications - rely on edge patterns to authenticate coins and prevent fraud. Even as digital payments increase, coins remain essential for small transactions, with the U.S. Mint producing approximately 11 billion coins annually. The continued use of reeded edges demonstrates how simple physical features can provide multiple layers of protection and utility in currency design.