http://www.behindthename.com/faq.php?type=names#junior
" Junior is used to distinguish a son with the same name as his father. The following conditions apply:
1. The Junior must be a son of the father, not a grandson.
2. The names must be exactly the same, including the middle name.
3. The father must still be living.
'II' is used whenever any close relative, including for example a grandfather or a great-uncle, shares the same name as the child. "
- mirfak