Reference

U.S. mint error guide

The error classes the identifier looks for on every scan — what causes each one, how to confirm it by eye, and what it does to value.

8 error types

Doubled die

Die

The die itself received a misaligned second impression during manufacture, so every coin struck from it carries the same doubling.

How to spot it: Look for clear separation and rounded edges on the date, lettering or motto. True doubling is raised and shows a full second image, not a flat smear.
Value impact: The strongest doubled dies are the most valuable U.S. error class, with premiums from a few dollars to five figures.
Known examples: 1955 Doubled Die Lincoln Cent · 1972 Doubled Die Obverse Cent · 1995 DDO Cent

Mint mark

The mint mark was hand-punched more than once, leaving a secondary letter offset north, south, east or west of the primary.

How to spot it: Under magnification the mint mark shows a ghost outline or a doubled serif offset in one direction. Direction is described by compass point.
Value impact: Usually a modest premium, but well-known varieties command strong collector demand.
Known examples: 1909-S/S VDB Lincoln Cent · 1960-D/D Small Over Large Date

Strike

The planchet was not seated in the collar, so part of the design lies outside the struck area.

How to spot it: A blank crescent along one edge with the design pushed to the opposite side. Value depends on how far off-centre it is and whether the full date shows.
Value impact: Coins that are 50% off-centre with a complete visible date carry the largest premiums.
Known examples: Any denomination, most common on cents and nickels

Strike

The retaining collar failed, letting the metal spread outward during the strike.

How to spot it: The coin is wider and thinner than normal, fully centred, with no reeding on the edge.
Value impact: Modest premium; larger and more dramatic spread means more value.
Known examples: Collarless quarters and dimes

Planchet

The blanking press overlapped a previously punched area, so the blank came out with a curved or straight bite missing.

How to spot it: A smooth curved or straight missing arc, plus the tell-tale weakness in the rim opposite the clip (the Blakesley effect).
Value impact: Small to moderate premium depending on size and denomination.
Known examples: Curved clip cents · Straight clip nickels

Planchet

A blank intended for another denomination or composition entered the press, giving a coin with the wrong weight and colour.

How to spot it: Weight is well outside the reference tolerance and the colour or diameter looks wrong for the type.
Value impact: Among the highest premiums; weight verification is the primary authentication test.
Known examples: 1943 copper Lincoln Cent · 1944 steel Lincoln Cent · Cent struck on a dime planchet

Die

A fatigued die cracks or loses a chunk at the rim; metal flows into the void leaving a raised line or blob.

How to spot it: A raised (never incised) jagged line across the field, or a solid raised lump joined to the rim for a cud.
Value impact: Small premiums for cracks; rim cuds are scarcer and more valuable.
Known examples: Late-die-state cents and half dollars

Strike

Debris packed into the die recesses blocked metal from filling the design.

How to spot it: Missing or mushy letters and digits with a smooth, slightly sunken surface — not the sharp separation of a real doubled die.
Value impact: Usually minimal; often confused with more valuable die varieties.
Known examples: Weak or absent mint marks and dates