Left coin without shoulder, right with shoulder.
The bead - the raised edge of a coin or medal , is part of the edge and field of the coin. It happens both on the obverse and on the reverse . It is a protection against wear of the relief of the coin . On some modern American and Australian coins, it also serves as a determinant of the coin value for blind people.
Sources
Numismatic Dictionary . Archived on May 19, 2012.