Machine Doubling

What it is

Machine doubling (also called mechanical or strike doubling) happens at the instant a coin is struck: a loose die bounces or twists slightly while still touching the coin, shoving the freshly struck design sideways. Instead of a true second image, the edges of letters and numbers get sheared into a flat, shelf-like step. It's incredibly common on modern coins, and it is not the same thing as a doubled die, because it's a one-off press hiccup rather than a flaw in the die itself. We include it here mostly so you can recognize it and not get fooled.

How to spot it

Look at the doubled area under a loupe and judge its shape: machine doubling is flat, low, and shelf-like, as if the edge of the letter was pushed over and smeared, and it often makes letters look thinner than normal. True doubled die doubling is raised, rounded, and full-bodied, with notched corners, and doesn't thin the letters. Machine doubling also tends to be shiny where the metal sheared. If the doubling looks like a step rather than a second letter, it's machine doubling.

What it's worth

Essentially zero. Machine doubling adds no meaningful value — dealers see thousands of these. Learning to tell it apart from real doubled dies will save you money and embarrassment, which is why it's worth studying anyway.

Famous examples

• 1955 'Poor Man's Doubled Die' Lincoln Cent (machine doubling, not a true DDO)
• Machine-doubled mint marks on 1960s-1980s coins