What's the difference between regular ACDelco and ACDelco Professional ?
http://www.rockauto.com/en/moreinfo.php?...n=18&jsn=18
http://www.rockauto.com/en/moreinfo.php?...n=23&jsn=23
http://www.rockauto.com/en/moreinfo.php?...n=18&jsn=18
http://www.rockauto.com/en/moreinfo.php?...n=23&jsn=23