Some die errors may be confused as die cracks, but there is a difference. A raised, thin, jagged line is attributed to a crack in a die, while a thick raised line occurs with a damaged die. When debris enters the stamping process, the debris may make an impression on the die head. Subsequent coins minted will show a thick line of material raised on the surface of the coin. If a hub is damaged, a similar line of material will appear on the surface of coins minted with dies prepared from a damaged hub. The first coin will have an indent on the coin's surface as the dies are pressed together to crush the debris into the coin's surface. Many of these coins are passed up by collectors as manmade damage, but there is a difference. Most manmade damage on the surface of a coin is created by scratching or gouging the coin and is easily recognized.
By Stan McDonald - Author and Numismatist