Ron Guth: Some 1794 and 1795 Silver Dollars are found with a silver plug in the center. The plug usually shows up as an area with a different color than the rest of the coin, indicating that the purity of the silver in the plug may differ than that of the rest of the coin. Experts believe that the plugs were used to bring a lightweight planchet up to the proper weight. This was done by drilling a hole in the center of the blank and inserting a silver plug of sufficient weight. During the striking process, the plug became flattened and an integral part of the coin. This process is similar to that seen on the 1792 Silver-Center Cents (Judd-1). At least one Silver-Center Cent is known without the plug (it was either never inserted or it fell out), but no 1794 or 1795 Silver Dollars are known without the plug.
Silver plugs appear on some varieties and not others, though new examples are discovered with some regularity. Beware of coins which have been treated to give the appearance of a silver plug. Normally, but not always, there should be a separation (albeit tiny) between the plug and the coin along some portion of the border of the plug.
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