Wrong die or mule

The coin error type of Wrong die or mule is a striking error that is commonly caused by an incorrect installation of the dies on the money press. This error occurs when a worker installs a pair of mismatched dies and activates the monetary press, resulting in the production of the so-called “mule” coins.

In numismatics, a mule is a coin that has designs on the obverse and reverse that are not normally seen on the same piece. This error can be intentional or caused by the negligence of the money press employee. Many varieties of this error exist internationally, and the number of possible combinations of different die pairs that can be installed (deliberately or negligently) from all the available dies within a mint is extensive. The final product will always be a coin that does not adhere to the characteristics of the issue decree.

There are different types of mule errors. Some coins may have the reliefs of the obverse or the reverse on both sides (pseudo-mule), while others may have one side with the reliefs of a nation and on the other the reliefs of another foreign nation (international mule). Transition mules occur when the imprints of one or both sides are changed in a year for a given coin.

It is essential to note that the incorrect installation of dies can result in significant consequences, and it is imperative to ensure that the dies are appropriately installed before the minting process begins.