The US Mint strikes their coins in what is called "coin turn". In other words, if you turn the obverse of a coin on a 12:00/6:00 axis, the reverse will be inverted (upside down). Many other countries strike their coins in what is called "medal turn". In other words, if you turn the obverse of a coin on a 12:00/6:00 axis, the reverse will be right side up. Chris