Ever since the U.S. Mint started producing coins in 1792, our
domestic issues have been struck with “coin rotation.” In other words,
the obverse face points north while the reverse face points south.
Significant deviations from coin rotation are considered errors. A
perfect 180-degree rotation is called “medal rotation” since medals
are minted with both faces pointing north. Medal rotation is normal
for some foreign issues, especially those produced by the United
Kingdom and its former colonies.
Rotated die errors can affect the hammer die (the die that
delivers the impact) or the anvil die (the die that absorbs the
impact). In most cases, it is impossible to determine which die
rotated. However, if combined with a second error (e.g., a horizontal
misalignment, a vertical misalignment, or a “one-sided” double
strike), the malpositioned die can sometimes be identified, and it is
almost always the hammer die.
Rotated die errors arise in three basic ways:
(1) A die is incorrectly installed.
(2) An improperly positioned “flat” is ground into the die shank.
A flat is a guide mark that helps position the die. If the flat is
ground in the wrong spot relative to the design on the die face, it
may lead to incorrect installation.
(3) A die can work its way loose and spin on its vertical axis.
The first two scenarios will result in a stable (fixed, static)
rotated die error. The third scenario will result in a dynamic rotated die.
A stable rotated die error is one in which the die (and each coin
it strikes) maintains the same degree of rotation throughout the
entire press run. A dynamic rotated die error is one in which the die
slowly spins or oscillates on its vertical axis so that most of the
coins it strikes show a different amount of rotation.
The situation is actually a bit more complex than what I’ve
portrayed. Some dynamic rotated die errors show an unusually narrow
range of positions or are dominated by a single position. It seems
that sometimes a rotating die will “freeze.”
Occupying this nebulous category of semi-stable rotations is an
extensive series of Jefferson 5-cent coins struck in 1966 (see photos
and the June 21, 2010, “Collectors’ Clearinghouse”). The vast majority
of these coins exhibit a 90-degree clockwise rotation, as shown.
However, a small number of coins struck by this die pair show lesser
degrees of rotation. Two members of the latter cohort are shown here,
one with a 20-degree clockwise rotation and one with a 40-degree
It is unclear why the die froze in a 90-degree position for so
many strikes. Perhaps it was installed in this position and then
worked its way loose. Perhaps it spun for awhile and then, when the
press operator noticed the problem, it was tightened down in the wrong
position. Or perhaps it simply became jammed in this position. It’s
also unclear why the full range of positions only occupies a quarter circle.
Some rotations long thought to be stable have instead been found
to be semi-stable once a larger sample was accumulated. The dies that
struck the two illustrated 1994 Lincoln cents produced a large number
of examples with a consistent 165-degree counterclockwise rotation
(shown in the second column). This is the only position listed for
this date in the Rotated Die Coin Census (www.rotateddies.com). I had
assumed it was a stable die rotation error and reported it as such in
the Collectors’ Clearinghouse column cited earlier. However, I’ve
since become aware of a smaller subpopulation with a 170-degree
clockwise rotation (shown in the third column). There also seems to be
a third, even smaller subpopulation, one characterized by a 180-degree
rotation. This third position was reported in a March 10, 2011, thread
that may be found on the Lincoln Cent Resource forum (www.lincolncentresource
Once again it is unclear why the die should rotate or oscillate
through such a narrow range of positions or why it should settle in
two primary positions.
It would seem that any claim of a stable rotated die error should
be tempered by the realization that a larger sample might reveal the
presence of other positions.
Coin World’s Collectors’ Clearinghouse department does
not accept coins or other items for examination without prior
permission from News Editor William T. Gibbs. Materials sent to
Clearinghouse without prior permission will be returned unexamined.
Please address all Clearinghouse inquiries to email@example.com or to
800-673-8311, Ext. 172.