Repunched Mint Mark
(abbreviated - RPM)
Until recently, all dies were made at the main U.S. Mint facility in Philadelphia. In the early years of production at the branch mints in San Francisco and Denver, dies were shipped from Philadelphia to these branch mints as they were needed. Before shipping them, a worker at the Philadelphia mint would use a tap and die set to punch a letter under the date designating the initial of the production facility where the die was to be shipped, thus all coins minted with that die would bear the letter of the mint. This letter is known as a "mint mark". Hand punching mint marks into the dies offers a chance for human error. Sometimes a mint mark would initially be placed improperly and had to be filled, then repunched. Sometimes the tiny mint mark punch would bounce while the mint worker tapped on it to impress the letter into the die. In these cases (and others like them) the mint mark in the die (and all coins minted with that die) would carry a doubled appearance. This effect is called a "repunched mint mark" (RPM).
The practice of hand punching mint marks into the individual working dies continued until 1990 when the mint decided to start placing the mint mark into the master die. Since there are many fewer master dies than working dies they could be inspected closely before creating hubs from them. This virtually eliminated all possibility for RPMs to happen, and so, ends an era in variety collecting.
To learn more about Repunched Mint Marks, click on the Coppercoins link below. Courtesy of Coppercoins.com