Look closely at the rim of a dime, and you will find an intricate series of raised vertical ridges known as reeds. The United States Mint mandates exact reeded edge specifications: every standard dime features precisely 118 reeds circling its perimeter.
Reeding originated in seventeenth-century Europe to defeat "clipping," an illicit practice where individuals shaved minute slivers of gold or silver from coin perimeters before passing them along at face value. While modern fiat coins lack precious metals, edge reeds remain standard for two distinct operational reasons:
First, reeding provides tactile differentiation. Visually impaired handlers can immediately differentiate a dime from a penny by running a fingertip along the rim. The cent is smooth-edged; the dime is rough.
Second, the ridges assist high-speed mechanical validation. Vending mechanisms and sorting machinery deploy optical and tactile sensors that gauge edge roughness and edge thickness simultaneously. A blank metal slug lacking the distinct 118-groove pattern drops into reject bins within fractions of a second.
