A partial collar error — sometimes called a "railroad rim" — occurs when a coin is struck with the collar die only partially engaged. Part of the coin shows normal edge detail (reeding or smooth edge), while the rest of the coin expands outward where the collar wasn't constraining it. The result is a coin with a stepped or tiered edge: normal on one portion and expanded with a fin-like ridge on the other.
The collar die is a ring that surrounds the planchet during striking, containing the metal to the correct diameter and impressing edge detail. When the collar is stuck partway up or down, mispositioned, or tilted, part of the planchet is within the collar and part extends above or below it. The constrained portion strikes normally; the unconstrained portion spreads outward.
These errors are best identified by examining the coin's edge. When photographing for ErrorHunt's scanner, try to capture the edge profile as well as both faces so the stepped or finned edge is visible.
A partial collar error occurs when the collar die that constrains a coin during striking is only partially in position. Part of the coin strikes normally within the collar, while the rest expands outward, creating a coin with a stepped or shelved edge.
The sharp, raised shelf on the expanded portion of the coin resembles a miniature railroad track or rail, giving these errors their nickname. The raised edge is distinctly different from the normal rim on the rest of the coin.
Partial collar errors are moderately uncommon. Minor collar slippage may go unnoticed, but dramatic partial collars with significant edge differences are genuinely scarce and attract collector interest.
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