why do quarters have ridges

Quarters have ridges, also called reeded edges, primarily to prevent a practice known as coin clipping. Coin clipping involved shaving off small amounts of precious metal from the edges of coins, which could then be collected and sold, while the clipped coin was still used at full face value. This practice was common when coins were made from valuable metals like silver or gold. Ridges on the edges of coins make it evident if any metal has been shaved off, as clipping would disrupt the pattern of ridges, thereby deterring fraudsters. This method of adding ridges to coin edges was introduced in the late 17th century, credited to Isaac Newton when he was the Warden of the Royal Mint in Britain. While circulating coins today generally no longer contain precious metals worth clipping, the ridges remain as a traditional feature and also help deter counterfeiting by making coins harder to replicate accurately.