This is the so-called Die Cap error. It occurs during forging, when the coin gets stuck in the stationary part of the mold, i.e. the anvil, and the forging continues. Then this distortion of the coin occurs, so that it resembles a lid or cork. Other coins, struck until this one was removed from the press, have a very faint impression of the obverse of this coin on the reverse. Such errors are extremely rare with our EX YU coins.

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