Tire offset on factory rims?

[sharpshooter33 at roadrunner.com (David Brown)]

I was wondering if the ET number on this webpage indicates offset?
http://www.vintagewatercooleds.com/tech/Techtips/Timbotechnotes/wheels/wheels.htm

I think I am beginning to understand offset, but I was wondering what about the center hole. Is that hubcentric?  I read something about spacers there to center the axles?  I guess they make rings to take up the slack?

Also does anyone have a list of the factory rims offset? I'm assuming they are around 38mm with the standard size 6" rims (snowflakes, scala, teardrops)?   That would mean if I've got 7" rims with 40mm offset they will stick out from the fender farther. I think this would explain why I get fender rub with my 195/60/14s

David