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Hub doubling, often called a doubled die, is created during the die-making process when a hub impresses a design into a die and the design images do not align perfectly. The result is not doubling added during the strike; it is doubling carried on the die itself. Every coin struck by that die will show the same raised design doubling in the same places.
Important distinction: machine doubling, strike doubling, die deterioration doubling, and other forms of worthless doubling are not hub doubling. Genuine hub doubling is normally raised and rounded like the rest of the design, and it often produces split serifs, notched corners, separation lines, or unusual extra thickness.
Quick Reference
| Class | Name | Primary idea |
|---|---|---|
| 1 | Rotated Hub Doubling | The hub or die rotates between hubbings, usually around a central axis. |
| 2 | Distorted Hub Doubling | One hubbing differs in size or shape from another, often tied to expansion or contraction of the hub or die during heat treatment. |
| 3 | Design Hub Doubling | Two different hubs, or two versions of a design, are impressed into the same die. |
| 4 | Offset Hub Doubling | The centers of the two hubbings are offset in one direction without a major rotational component. |
| 5 | Pivoted Hub Doubling | The hub or die rotates around a pivot point located near the rim instead of near the center. |
| 6 | Distended Hub Doubling | A lateral expansion or stretching of the die face occurs during hubbing, affecting parts of the design as the steel moves. |
| 7 | Modified Hub Doubling | Historically described as doubling caused by a hub that was modified, leaving remnants of an earlier design element. |
| 8 | Tilted Hub Doubling | The hub is tilted relative to the die during hubbing, causing partial or uneven design transfer. |
| 9 | Single-Squeeze Hub Doubling | A modern single-squeeze hubbing press allows the hub to start slightly tilted or loose, then jolt, rock, or roll into position during the single hubbing. |
Class 1: Rotated Hub Doubling
How it happens: The hub or die rotates between hubbings, usually around a central axis.
What to look for: Doubling shows a clockwise or counter-clockwise spread. Rounded secondary images, split serifs, notched corners, separation lines, or extra thickness may be visible. Classic Lincoln cent examples include 1955 DDO-001, 1969-S DDO-001, and 1972 DDO-001.
- Attribution tip: Check whether the spread follows a rotational pattern around the center of the design, not merely a flat shelf pushed to one side.
Class 2: Distorted Hub Doubling
How it happens: One hubbing differs in size or shape from another, often tied to expansion or contraction of the hub or die during heat treatment.
What to look for: The spread usually appears near the outer devices and tends to move toward the rim or toward the center. It is most obvious in design elements near the periphery. Look for outward or inward movement that is not primarily rotational.
- Attribution tip: Compare the direction of spread around the perimeter; Class II should suggest size distortion rather than a pivot point.
Class 3: Design Hub Doubling
How it happens: Two different hubs, or two versions of a design, are impressed into the same die.
What to look for: The doubled element reflects a design difference rather than a simple misalignment. This can include large-date/small-date combinations, proof/business-strike hub differences, or twentieth-century hub-created overdates such as 1942/41 dimes and 1943/2 Jefferson nickels.
- Attribution tip: Ask whether the doubled feature is actually a different design element, not just the same element shifted.
Class 4: Offset Hub Doubling
How it happens: The centers of the two hubbings are offset in one direction without a major rotational component.
What to look for: The doubling is usually spread evenly in one direction. It often appears closer to the center than the rim, may show rounded extra images, and can show notching on letters or numbers.
- Attribution tip: Look for a consistent one-direction offset without the fan-shaped falloff of Class V.
Class 5: Pivoted Hub Doubling
How it happens: The hub or die rotates around a pivot point located near the rim instead of near the center.
What to look for: The strongest spread is opposite the pivot point and fades as you move toward the pivot. It is related to Class I, but the uneven distribution of spread is the key diagnostic. The 1995 Lincoln cent DDO-001 is a well-known example.
- Attribution tip: Find the quiet side. If the spread fades toward one rim area and strengthens opposite it, suspect pivoted doubling.
Class 6: Distended Hub Doubling
How it happens: A lateral expansion or stretching of the die face occurs during hubbing, affecting parts of the design as the steel moves.
What to look for: Design elements, especially near the rim, may look thickened, stretched, sloped, pointed, twisted, or distorted. It often resembles Class II but tends to have a more stretched or swollen character.
- Attribution tip: Do not demand clean separation lines; thickness and distortion can be the main evidence.
Class 7: Modified Hub Doubling
How it happens: Historically described as doubling caused by a hub that was modified, leaving remnants of an earlier design element.
What to look for: This class is controversial and rare in practice. Some older attributions have been reclassified. CONECA notes modern Class VII use mainly around specific 1941 Lincoln cent cases involving a normal hub and a broken-T hub.
- Attribution tip: Use caution. Older Class VII claims should be checked against current attribution references because several have been re-evaluated.
Class 8: Tilted Hub Doubling
How it happens: The hub is tilted relative to the die during hubbing, causing partial or uneven design transfer.
What to look for: Doubling is often partial and may appear on only a portion of the design. It commonly trends inward toward the center and may be accompanied by minor offset, pivot, or rotational effects.
- Attribution tip: Partial, localized doubling may be meaningful when the affected area fits a tilt pattern rather than strike damage.
Class 9: Single-Squeeze Hub Doubling
How it happens: A modern single-squeeze hubbing press allows the hub to start slightly tilted or loose, then jolt, rock, or roll into position during the single hubbing.
What to look for: Often found in central design areas, though it can be broader. CONECA describes two broad appearances: jolted doubling, focused in a hot zone with duplicated elements in nearby fields; and roly-poly doubling, with soft, offset, swollen extra thickness.
- Attribution tip: Modern single-squeeze varieties often appear in central design hot spots; do not dismiss them simply because there was only one hubbing.
Practical Identification Checklist
- Confirm the doubled feature is raised and rounded, not flat, shelf-like, or scraped-looking.
- Look for split serifs, notched corners, separation lines, or thickened devices that repeat from coin to coin.
- Map the direction of the spread. Rotation, offset, pivot, distortion, tilt, and single-squeeze jolting each leave a different pattern.
- Use die markers only as supporting evidence. They help confirm a listed variety, but they do not create the variety.
- Remember that a doubled die is a die variety. A single damaged coin, no matter how dramatic, is not automatically a doubled die.
Notes on the Ninth Class
Collectors should know that not every attributer handles Class IX the same way. Many traditional references recognize eight classes and fold modern single-squeeze doubled dies into the earlier framework. CONECA and CopperCoins usage recognizes a ninth class for doubled dies produced in single-squeeze hubbing presses. That difference is not merely academic; it affects how a modern doubled die is described and cataloged.
Sources Consulted
- CONECA, “The 9 Classes of Doubled Dies.”
- Wexler Doubled Die Files, “Doubled Dies.”
- Error-Ref.com, “Doubled Dies” and die-variety class references.
