With the emphasis now on error coins, thanks in part to coin microscope sales and hyperbolic coin values on social media, it is important to know the difference between machine and hub doubling.
This is a tutorial.
Let’s start with a photo showing a machined v. hub doubled 1969-S cent. Both look significant. Only one is. Can you tell the difference? (We’ll return to these coins momentarily.)
Machine doubling, the above left photo, adds no or little value to coins. It happens when a die at the Mint begins to deteriorate and so may bounce during a strike, creating a flat shelf-like image. The date, device, lettering and mintmark can appear to be doubled.
Why do most coins have machine doubling? Because the U.S. Mint uses working dies as much as possible before changing them, as a cost-effect practice.
Hub doubling, valuable, indicates a flaw in the die itself. Unlike machine doubling, which happens during a strike, someone at the Mint made an etching mistake. Mintmarks before 1989 were punched into the die; but this is distinct from hub doubling. We call these deviations “repunched mintmarks” (RPM). Hub doubling produces a raised, rounded impression that follows the flow of the date, lettering or device.
Let’s illustrate this again more closely with the 1969-S DDO cent, one of the most illusive coins, worth a bundle. It is ultra rare with PCGS holdering only 30+ coins. You can read about that here.
Clickbait social media says you can find one in pocket change. Oh, and you’ll need to buy a coin microscope for that. Fat chance.
New collectors who routinely consult social media for any number of topics often believe these hyped posts. Odds are you will never find a 1969-S DDO in rolls or pocket change. But you can find dozens of machined doubled ones on eBay and elsewhere masquerading as an authentic 1969-S DDO with sellers asking hundreds and thousands for a faux coin:
Let’s return to the images mentioned earlier and show distinctions between machine doubled and authentic doubled dies:
Machine Doubling, Left; Hub Doubling, Right
The machine doubled cent has a flat, shelf-like doubling. The doubling does not mirror the individual numbers but seem pushed to the right. The hub doubled cent has raised rounded digits that follow the contours of the numbers.
In addition to the ability to distinguish between machine and hub doubling, veteran collectors know how to identify replicas flooding the market from China. You can buy these fake ultra rarities on venues like Etsy for less than $30.
These replicas are purchased by scammers and then posted on eBay as the real deal. Now you have to compare devices with genuine coins. To do that, google a genuine one in a PCGS holder and compare doubled devices.
The obvious difference is the word “Liberty.” Take a closer look:
The doubling on the replica is mushy and below the original letters of “Liberty”; the doubling on the authentic coin is above “Liberty” with each letter mirroring the original and shifted to the right.
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