Strike-Through (STT)

A strike-through error occurs when a foreign object is caught between a die and the planchet at the moment of striking. The object prevents the die from fully impressing the design into the coin's surface in the area it occupies, leaving an incuse impression of the foreign object — or a blank, design-free depression — on the finished coin. Strike-throughs have been documented with a wide variety of foreign materials: grease, cloth, string, wire, metal fragments and shavings, plastic, hardware and more. NGC has called struck-throughs perhaps the most common type of mint error.

The term "strike-through" encompasses a broad family of errors united by a single mechanism — something was between the die and the planchet that should not have been there. The visual result varies dramatically depending on the material, size, and position of the foreign object.

How Does It Happen?

The minting environment is a high-speed industrial operation. The U.S. Mint gives 750 coins per minute for a circulating-coin press, and planchets are fed and ejected by automated mechanisms. Within this environment, foreign material can reach the striking surface through several pathways:

• Die fill ("grease"): The recesses of a die (which produce the raised design on the coin) can clog with compacted material that Error-Ref describes as generally a mix of lubricant, metal dust and dirt. Collectors call it "grease" or "die fill". When these recesses fill, the design cannot transfer to the planchet. The result is known as a filled die or struck-through-grease error.
• Cloth and textile fibers: Pieces of cloth, thread, or fiber from cleaning rags, gloves, or industrial wipes can land on the die face or planchet. The fiber is pressed into the coin's surface during striking, leaving a linear or curved impression.
• Metal fragments: Small pieces of metal — from planchet edges, die chips, or press components — can fall onto the die or planchet. These produce sharp, defined impressions in the coin's surface.
• Wire and staples: Pieces of wire occasionally reach the striking chamber. Wire strike-throughs leave distinctive thin, curved or straight-line impressions.
• Other debris: Error-Ref lists strike-throughs of string, plastic, hardware, metal dust and shavings, and pieces of clad layer, among others.

Once the foreign object is in position, the press cycle proceeds normally. The dies close with full force, and the object is squeezed between the die and planchet. The die impresses the design everywhere except where the object blocked it. The object usually falls away after the strike, though sometimes it remains embedded in the coin's surface. Error-Ref calls this a retained struck-through (or "struck-in") error and notes that the most common retained objects are pieces of scrap coin metal.

How to Identify a Strike-Through

Strike-through errors are identified by the impression left by the foreign material:

• Incuse impression in the design: An area of the coin's surface shows a depression, void, or foreign-object outline where the design is absent or incomplete. The surrounding design is normal.
• Object-specific shape: The impression matches the shape of the foreign object. Thread strike-throughs show a linear or curved threadlike impression. Wire strike-throughs show a thin metallic line. Grease strike-throughs show a smooth, filled-in area.
• Smooth or textured depression: Depending on the material, the impression may be smooth (grease, plastic) or show surface texture (cloth weave, metal grain).
• Design absence, not damage: The missing design in a strike-through area was never struck — the die could not reach the planchet. This is different from post-strike damage where design was struck but later removed. A strike-through shows smooth, original-surface metal in the depression; post-strike damage shows scratches, tooling marks, or rough metal.
• Single-sided: The strike-through affects only the side where the foreign object was positioned. The opposite side of the coin is typically normal (unless foreign material was present on both dies simultaneously).

Common Strike-Through Types

Grease-Filled Die

Grease-filled die errors are the form of strike-through most collectors meet first. The die's recessed areas gradually fill with compacted die fill during a production run. As it accumulates, it prevents design transfer to the planchet. The result is a coin with portions of the design smoothly filled in or missing entirely.

Common grease-filled die presentations:

• Partial date: One or more digits of the date are filled or weak because grease accumulated in the date area of the die
• Missing letters: Individual letters in legends (LIBERTY, IN GOD WE TRUST, E PLURIBUS UNUM) are absent or ghostly
• Featureless portrait: Portions of the main design element (Lincoln's hair, Washington's profile) are smoothed away

Grease-filled die errors range from minor (a single weak letter) to dramatic (virtually the entire design missing from one side). Error-Ref notes that a coating can be thick enough to obscure the entire design, and illustrates a 1984 Lincoln cent with both faces partly obscured.

Notable Examples

Struck Through Cloth

Cloth strike-throughs have a distinctive appearance: the weave pattern of the fabric is preserved in the coin's surface, creating a textured, grid-like impression. The cloth texture is unmistakable under magnification.

Struck Through Wire and Staples

Wire strike-throughs produce thin incuse lines across the coin's surface. The wire's circular cross-section creates a distinctive rounded channel. Staple strike-throughs show the characteristic U-shape of a wire staple impressed into the metal.

Field-Restricted Strike-Through

A field-restricted strike-through occurs when foreign matter is confined exclusively or primarily to the field portion of the die face — the flat background area between the raised design elements. The result is a coin with pitting, channeling, or texture disruption across the field, while the raised design (portrait, lettering, date) remains largely unaffected.

Field-restricted strike-throughs typically display a consistent directional pattern across the affected area. The pitting and channels follow a uniform orientation because, as Error-Ref explains, the gritty paste is spread onto the die face by a feeder coated with it, and the pattern mirrors the feeder's movement. This directionality distinguishes field-restricted strike-throughs from random post-strike damage, which shows no organized pattern.

The foreign matter involved is often a gritty or paste-like substance rather than a single discrete object. Under magnification, the affected field shows a rough, textured surface — sometimes described as having a chunky or granular appearance — with shallow surrounding areas where the substance spread thinner. In some cases, field-restricted strike-throughs co-occur with die scrapes running in the same direction, confirming that both features were caused by the same material being dragged across the die face.

Field-restricted strike-throughs are more common on the face struck by the anvil (lower) die. However, they can appear on the face struck by the hammer die, and in some cases both sides of the coin are affected simultaneously. Error-Ref illustrates 2007 and 2008 Lincoln cents with virtually identical patterns on the obverse, which on those coins was struck by the anvil die; the northwest-to-southeast orientation of the pits and channels is consistent from die to die.

Dropped Fillings

A dropped filling occurs when accumulated die fill -- hardened grease, compacted debris, or other material that has built up inside a recessed area of the die -- dislodges as a solid chunk and lands on a planchet or die face. When the next strike occurs, the chunk is pressed into the coin's surface, leaving an incuse (sunken) impression where the filling was squeezed between the die and the planchet.

The impression often takes the shape of the design element whose die recess the filling had accumulated in. A filling that built up inside a letter or digit drops out as a roughly letter-shaped or digit-shaped plug, and the struck impression reproduces that shape in incuse form. If the plug remains next to the same die recess it fell from and does not flip over, the incuse impression appears in normal orientation alongside the properly struck version. If the filling contacts the opposite die or flips before striking, the impression appears mirror-image reversed. Error-Ref notes that most dropped fillings are normally oriented, and that letters and numbers are the elements most often reproduced this way; its examples include a 1965 cent with a dropped A from the reverse and a 2006 cent with a dropped urn from beside the Memorial steps.

Dropped fillings can land anywhere on the coin's surface -- near their original position, in the field, or on an unrelated design element. The impression may be a recognizable letter or digit shape, or it may appear as an irregular incuse depression depending on how the filling deformed before or during the strike.

Dropped fillings are sometimes found retained (the filling material still attached to the coin) and sometimes leave only the incuse impression where the chunk was pressed in and then fell away. When the filling is retained, the material itself helps confirm the error's origin.

Struck Through Die Cap

A struck-through die cap is a strike-through error where the foreign object interposed between the die and the planchet is another coin -- specifically, a coin that has adhered to the die face and formed a die cap. Every coin struck while the cap is on the die is a struck-through-die-cap coin, receiving its impression through the metal of the cap rather than directly from the die.

Early in the cap sequence, the stuck coin's design is still sharp and impresses recognizable detail as a brockage (mirror-image incuse impression). As the cap is stretched and thinned by repeated strikes, the transferred design becomes progressively fainter until only ghost impressions or no design at all comes through. At that late stage, the cap is functioning as a featureless metal barrier -- a strike-through in the most literal sense.

Struck-through-die-cap coins are distinct from the die cap itself, which is the single coin that stuck to the die. See the Capped Die page for the full explanation of how caps form, the difference between obverse and reverse die caps, and how to identify both the cap and its struck-through products.

"Blank" Coins from Extreme Grease Fill

When grease fills virtually all of a die's recessed areas, the resulting coin shows almost no design — just a smooth, blank disc with faint traces of the highest-relief design points. These extreme grease-filled die errors are sometimes mistaken for unstruck planchets, but they show several distinguishing characteristics: they have an edge formed by the collar (reeded on a reeded-edge denomination) and a full-diameter rim, and they exhibit faint design traces at the highest points.

Collecting Tips

• Identify the material: The shape and texture of the impression usually tell you what the object was — smooth fill, cloth weave, a round-section wire, a sharp-edged metal fragment.
• Size and visibility: Record how much of the surface the strike-through covers and whether the object's detail can be identified.
• Design preservation: A strike-through that hides the date or mint mark makes the coin harder to attribute. NGC notes that a coin with most of its design obscured by grease cannot receive a numerical grade and is labelled as a mint error instead.
• Object retained in the coin: Occasionally, the foreign object remains embedded in or attached to the coin after striking. Error-Ref notes that a retained object is usually set off from the coin by a narrow fissure, that a sizable one pushes the weight beyond tolerance, and that such errors can be hard to tell from rolled-in errors.
• PCGS and NGC attribution: Both major grading services attribute strike-throughs on holder labels and identify the material when possible (e.g., "Struck Through Cloth," "Struck Through Wire").
• Examine with magnification: Many strike-throughs reveal their true nature only under a loupe or microscope. What looks like a smooth depression to the naked eye may show cloth weave, wire striations, or organic texture under 10x to 20x magnification.
• Not all missing design is a strike-through: Worn dies, die polishing, and weak strikes can also produce coins with reduced design detail. A genuine strike-through shows a defined boundary between the affected area and the surrounding normal design, and the affected area has a smooth, original surface rather than a worn or abraded one.