Master Die Doubling
When the master hub is used to make the master dies, it is pressed onto the master die surface with tremendous pressure. This process must usually be done more than once while the master dies are annealed in between presses. If the master hub and the master die become misaligned during this process it will create a doubled image on the master die. If the master die has a doubled image on it, every working hub made from that master die will also have the doubled image, then all of the working dies made using the doubled working hubs will also exhibit the same doubled image. Since several dies will have the exact same doubling and tens of millions of coins will be struck with these dies, they won't have any premium value over a common coin, as most coins minted that year will be the same.
Master Die Doubling List
Click on a year below to see the master doubling for that year.