51 Over 81

One major variety is the 1851/81 Braided Hair Large Cent (Penny) Overdate Error. This coin features an 1851 date struck over an inverted upside-down 1851 date. This resulted in the "51" being struck over an "81". One way to identify this coin is to notice a small portion of the underlying "8" on both sides of the "5" and parts of the underlying "1" around the upper portion of the overlying "1"