This glossary provides clear, collector‑friendly definitions of the most important mint error terms. Whether you’re new to the hobby or building an advanced reference library, these terms will help you understand how errors form and how to identify them.

🟦 A–C Terms

Annealing

The heating process used to soften blanks before striking. Improper annealing can cause discoloration or wrong‑metal appearance.

Blank

A round metal disc punched from sheet stock before it receives a rim. Not yet ready for striking.

Blakesley Effect

A weak or missing rim opposite a genuine curved clip. One of the strongest diagnostics for authentic clipped planchets.

Broadstrike

A coin struck without the collar in place, causing the design to remain centered but the coin to spread outward and lose its rim.

Capped Die

A coin that sticks to a die and becomes a “cap,” striking subsequent coins with a distorted, mushroom‑shaped impression.

Clip (Clipped Planchet)

A planchet missing a curved or straight section due to overlapping blanking punches or misfeeds. Shows the Blakesley Effect.

Collar

The metal ring that holds the planchet in place during striking and forms the rim. Collar failure causes broadstrikes.

Cud

A raised, blob‑like area on the rim caused by a piece of the die breaking off. Must touch the rim to be a true cud.

🟩 D–F Terms

Die

The engraved metal tool that strikes the coin’s design onto the planchet.

Die Break

A raised area caused by a crack or fracture in the die. If it does not touch the rim, it is not a cud.

Die Cap

A coin that sticks to a die and forms a cap shape. Produces brockages and distorted strikes on later coins.

Die Clash

When the dies strike each other without a planchet between them, transferring design elements onto the opposite die.

Die Crack

A thin raised line caused by a crack in the die. Common and usually low‑value unless dramatic.

Double Strike

A coin struck more than once. The second strike may be in‑collar, out‑of‑collar, or flipped over.

Feeder Finger Strike

Damage caused by the feeder mechanism, not a mint error. Often mistaken for errors by beginners.

🟧 G–M Terms

Grease‑Filled Die (Struck Through Grease)

A die clogged with grease or debris, causing missing or weak design elements.

Indent

A deep, curved depression caused by another planchet overlapping the struck coin.

Lamination Error

A peeling or flaking defect caused by impurities or bonding issues in the metal strip.

Misaligned Die

One die (usually the hammer die) is slightly off‑center. Does not produce a blank crescent like an off‑center strike.

Missing Clad Layer

A clad coin missing one of its outer layers, exposing the copper core.

🟨 N–S Terms

Off‑Center Strike

A coin struck with the planchet not properly centered between the dies, leaving a blank crescent.

Overstrike

A coin struck on top of an already‑struck coin of a different type. Rare and dramatic.

Planchet

A blank that has passed through the upsetting mill and now has a raised rim, ready for striking.

Rim Burr

A small metal fin caused by excessive striking pressure. Not a mint error.

Rotated Die

The obverse and reverse dies are misaligned relative to each other, causing rotated orientation.

Struck Through

A coin struck with a foreign object between the die and planchet (cloth, wire, debris, etc.).

Struck on Wrong Planchet

A coin struck on a planchet intended for a different denomination, metal, or foreign coin.

🟫 T–Z Terms

Transitional Error

A coin struck with the wrong metal composition during a year when the mint changed alloys (e.g., 1965 silver‑planchet dimes).

Uniface Strike

A coin struck with only one die, leaving the opposite side blank.

Weak Strike

Insufficient striking pressure, often caused by die spacing issues. Not always a mint error.

Wrong Stock

A coin struck on metal strip of the wrong composition but correct size. Related to off‑metal errors.

🏁 Final Thoughts

Understanding mint error terminology is essential for identifying genuine errors and avoiding altered coins. This glossary provides a solid foundation for collectors at every level and pairs perfectly with the detailed reference articles throughout ErrorCoins.com.