I never had a good lining, but I did have success on a 6.8mm and others have had success with a 6.5mm and up. Ideally you would want it much thicker of course but some of us just can't get there.
Check out this post for everything I tried:
http://www.network54.com/Forum/57451/thread/1282009934/Viva+Viagra%21%21%21
Hope this helps and best of luck to you.
Audrey