Rule when primary key is needed?

From: Roland Bengtsson (roland.bengtssonsf_at_home.se)
Date: 08/15/04 

Date: 15 Aug 2004 06:15:53 -0700

Is there a rule when primary key is needed in a table?
For example I have small tables with 5 - 20 posts. These are used with
Comboboxes in another table. I realize now that a key isn't needed in
the small tables.

/Roland