The regular dies trial piece. These were eiter deliberately struck for sale to collectors or are mint errors as described with each piece.
Examples were struck in the following combinations:
Copper J455/P529. These are presumably on thick planchets. They may actually be mint errors on bronze planchets that were of the wrong thickness. Only 2 or 3 are believed to exist.
Copper-Nickel J456/P530. These are believed to have been struck on leftover planchets used for regular coinage from 1857-1864 and thus may be mint errors. About a dozen are believed to exist including the illustrated example.
Nickel J457/P531. There is a strong possibility that these are also mint errors struck on stock intended for either regular nickel 3 cent or shield nickel coinage. One example was tested and found to be 80% Copper and 20% Nickel and weighing 47.84 grs which casts doubts on that theory, however. Only 2 or 3 are believed to exist.
Photo courtesy of Bowers and Merena.