plug nickel

Some early United States coins (minted in the 18th and 19th centuries) were made with a small silver disc added to the center of the coin in the planchet (blank metal) before striking. This was done to increase the value of the metal in the coin up to the coin's face value. A plug nickel or plugged nickel is a nickel (now a five-cent coin, but originally a one-cent coin and later a three-cent coin) where the "plug" (center disc) has been removed, thus decreasing the metal value of the coin. People would often examine their change after a cash transaction to ensure they did not receive such a coin.