How many sides are there to a coin? The answer that might immediately come to mind is two, but some argue that the edge is really the third side to a coin. While not nearly as visible as the obverse and reverse, a coin’s edge actually plays an important role. It can serve as a deterrent to counterfeiters, a way of differentiating various denominations, and a place to inscribe mottos or legends.

For as long as coins have been made of precious metal, there has been an unfortunate practice of scraping, clipping and shaving coins. The unscrupulous practice involves taking a coin made of silver, gold or platinum and removing a small but virtually undetectable amount of metal. The idea was that a small amount could be removed from a large number of coins—and the net amount of metal would be quite valuable.

Metal removed from the surface or the rim of a coin was generally easy to detect and spot visually. Thus, most clippers and scrapers targeted a coin’s edge instead. To combat this practice, mints began striking coins with reeded (grooved) edges. If a coin’s edge were smooth and missing its usual reeded texture, the coin would instantly be considered tampered.

In addition to underweight clipped coins, counterfeits have been a constant problem for centuries. Counterfeiters were usually able to replicate genuine coinage designs; their copies might have been crude but they usually approximated the original version. The edges, however, were quite difficult to copy. This was especially the case once mints started engraving lettering, designs and other complex elements on the rim. Most counterfeiters lacked the proper equipment to give coins simple edge designs, let alone complex ones.

In more recent years, world mints have largely discontinued making coins out of precious metals. They now favor low-value base metals like copper, bronze, zinc and nickel for everyday circulating coinage. With clipping and counterfeiting being less of an issue, one might wonder why some coins continue to have reeded edges. The grooves actually serve the practical purpose of differentiating the various coinage denominations by touch. By giving certain coins reeded edges (like the dime and quarter) while leaving others smooth (like the penny and nickel), it’s easier to reach into one’s pocket and immediately recognize which coin is which.

For bullion coins, using reeded edges remain standard practice. It should be noted that all United States silver and gold eagles continue to be struck with grooved edges. The US Mint feels relatively confident that pennies and nickels will not be subjected to clipping or counterfeiting—but high value bullion coins are still given every available protection.