Many types of mint errors are missed by inspectors and are inadvertently released into circulation. Clipped Planchets, Off-Center Strikes, and Wrong Planchets are just a few examples of the many types of error coins that slip out of the mint occasionally. Some errors are fairly common, but many are extremely rare.
Washington Quarter struck on a clad dime planchet. Full date!
1975 Lincoln Cent struck on a clad dime planchet.
Jefferson Nickel struck on a cent planchet.
Cent Struck Over a 2001-P Dime. Traces of the dime design are visible including the outline of Roosevelt's head and some of the under-type. A very exciting mint error!
Struck on a struck Lincoln Cent. Flip-flop strike. The under-struck Lincoln is easily seen. Rare, very high quality, and very cool!