What Does the copper rim do?

What does copper rimmed coins mean?

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Copper rim is common on clad dimes, quarters and half dollar coins minted after 1964. They are a nickel/copper alloy whereas those denominations 1964 and before were minted as 90% silver. There were some 1976 “Drummer Boy” quarters minted in 40% silver/60% copper. Those would not show the defined copper rim.