Are we talking about points to points? A 0.001 pt rule would probably not print--I'm not sure it would display properly unless zoomed in. Acrobat may be enhancing the preview.
Did you check the width with the Object Inspecter?
Are you sure the Fix Hairlines was not run as part of a preflight?
David Creamer: Community Expert (ACI and ACE 1995-2023)