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.
Indian Head Cent. Struck 15% off center.
1968-S Lincoln Cent. A proof that is struck on a dime planchet.
2001 Lincoln Cent struck over a Roosevelt Dime! The reverse under-type of the dime shows on the obverse and visa versa. An exciting Double Denomination error!
2002 Tennessee Quarter struck on a nickel planchet.
2002 Tennessee Quarter struck on a nickel planchet.