This mishap occurs when
opposing dies collide with each other when a planchet fails to be fed into the
striking chamber. Most complete planchet misfeeds don't result in clashed
dies because dies normally don't touch each other in the absence of a planchet.
The dies operate with a safety margin that can be referred to as minimum die
clearance or minimum die distance. These terms refer to the closest
approach the dies make to each other in the absence of a planchet. In
order for dies to clash, the dies must have fallen out of adjustment so
that their minimum clearance is zero (or less than zero).
1988 cent shows strong clash marks on both faces that persist even after
vigorous attempts to abrade them away by mint technicians. These clash
marks are also somewhat misaligned (horizontally) and slightly rotated.