I need to replace the fuel line just before the fuel filter. Brought this today: http://www.rockauto.com/catalog/moreinfo.php?pk=622474
My question is, what is that little rubber o-ring used for? I was in a hurry and as soon as i left i forgot to ask the guy what its use was for.
Thanks!

 

That o-ring is supposed to go on the end of the line that goes into the fuel filter; tt is what provides the seal between the line and the filter.

 

As stated, it was supposed to go over the end of the line to then go into the filter. The original didn't have an o-ring though which makes me think that the replacement you picked up isn't exactly correct for your application. It should still work though.