Doubled dies are a result of the way in which in the United States Mint's dies are created. Before 1997, die pairs (hammer die and anvil die) were made by hubs that contained the raised design elements that were intended to appear on the coin. The blank dies were heated (to soften them) and then were pressed against the hubs to transfer the design from the hub to the working dies. One impression was not enough in every case to transfer the design elements from the hub to the die, so multiple impressions were required to transfer enough of the design. For this reason, after the first impression was made, the die was reheated and prepared for a second impression. The mint workers would use guides to align the hub and the working die perfectly to prevent overlapping, or a doubled die. It is when mint workers failed to align dies properly during this process that doubled dies were produced. In many instances three to four impressions were required, which could but rarely led to tripled and quadrupled dies.