The nine-digit SSN is composed of three parts: 1  The first set of three digits is called the Area Number. 2  The second set of two digits is called the Group Number.3  The final set of four digits is the Serial Number.umber Has Three Parts. The nine-digit SSN is composed of three parts: 1  The first set of three digits is called the Area Number. 2  The second set of two digits is called the Group Number. 3  The final set of four digits is the Serial Number.