A “wrong stock” error is a coin struck on a planchet of the correct
diameter but punched out of coin metal strip intended for another denomination.
Shown here is a 1970-D Washington quarter
dollar struck on dime stock. It weighs 4.24 grams. While dime stock
quarter dollars can be found in many years between 1965 and 1992, the
1970-D coin is by far the most common date-and-Mint combination.
Our next coin, a 1974 Washington quarter
dollar, was also struck on an abnormally thin planchet. But at 4.92
grams, it is too heavy for dime stock. It’s a “rolled-thin” error. It
was struck on a planchet derived from copper-nickel clad quarter
dollar strip that was rolled too thin.
Weight is critical in distinguishing wrong
stock errors from rolled-thin and rolled-thick errors. And yet many
collectors, dealers and grading services pay only occasional attention
to this all-important component. Over the years I’ve encountered a
prodigious number of abnormally thin or thick coins that were
incorrectly labeled as “wrong stock.”
Because of the high frequency of misdiagnosis,
every collector should learn how to calculate the expected weight of a
suspected wrong stock error. The calculation is simple and requires
only basic algebra and geometry.
The general equation is written as follows:
weight of normal coin from suspected stock =
expected weight (X)
area of normal coin from suspected stock area of your
The area of a circle is calculated using the
formula πr2, or pi times the square of the radius. The radius is half
of the diameter. Coin diameters are found in many basic references and
on the U.S. Mint website (www.usmint.gov/about_the_mint/?action=coin_specifications
The value of pi is 3.14.It is not necessary to calculate the volume of
each planchet, as thickness is a constant. For a quarter dollar struck
on dime stock, the equation would be:
weight of dime = expected weight of dime
stock quarter (X)
area of dime area
of quarter dollar
2.27 grams =
3.14 × (17.91 mm ÷ 2)2
3.14 × (24.26 mm ÷ 2)2
Simplifying the denominator, the equation becomes:
2.27 grams =
251.8 square mm 462
Now cross multiply, to get: 251.8X = 1048.74.
Divide 1048.74 by 251.8.
X = 4.16 grams, the expected weight of a
copper-nickel clad dime stock quarter.
The weight of the actual coin may deviate up
to 0.15 gram from the expected weight. Deviations greater than 0.2
gram in either direction probably mean you’ve got a rolled-thin error
instead of a wrong stock error.
Coins such as this 1953-S Washington quarter
dollar are frequently misidentified as having been struck on dime
stock. It weighs 5.11 grams. It is one of many thin quarter dollars
produced by the San Francisco Mint between 1951 and 1954. A silver
dime stock quarter should weigh around 4.59 grams, but these coins all
fall between 4.9 and 5.4 grams.
In addition to weight, it is important to pay
attention to other features including composition and signs of uneven
thickness. For example, I have seen many encapsulated Kennedy half
dollars from the years 1965 to 1969 labeled as “quarter stock” or
“quarter thickness stock.” Besides being too heavy, their composition
is all wrong. Quarter dollars from this period have a copper-nickel
clad composition while half dollars have a silver-copper clad
composition. All of the “quarter stock” half dollars that I’ve
inspected, and that others have inspected on my behalf, have a normal
silver-copper clad composition.
A similar misdiagnosis was applied to the
abnormally heavy 1965 quarter dollar shown here. Weighing a hefty 7
grams (normal is 5.67 grams), it was labeled as having been struck on
“50c stock.” I have seen other heavy quarter dollars from this year
similarly labeled. And yet, instead of having the silver-copper clad
composition of half dollars from this period, it has the copper-nickel
clad composition of a normal quarter dollar. This is simply a
rolled-thick error. While the weight approximates that of a quarter
dollar struck on copper-nickel clad half dollar stock, it is probably coincidental.
Error dealer Jon Sullivan recently acquired
three thick 1965 quarter dollars whose weights were 6.53 grams, 6.83
grams and 6.91 grams. Two of the coins were struck by the same die
pair. The variability suggests that a roller was improperly adjusted
and that the distance between the rollers was fluctuating.
Wrong stock errors are best collected in their
raw state. Many purported wrong stock errors that are encapsulated
have no weight printed on the label. And even if a weight is included,
there’s no guarantee that it has been accurately recorded.