69chargeryeehaa, please forgive my faux pas. I have made the proper adjustments.-LOL

I have somehow become a tad confused on which rollers to use. I have found the 4 inch 'white foam' roller that is about one inch in diameter, but I have also found some that are two inches in diameter with the white foam. Which roller is the proper one?

On a side note- My 45 GMC COE was getting some bad rust and rust through in some places and my wife knew it would be some time before we could get to restoring it, so she and my daughter decided to paint it with a 'rust paint' call Zero Rust. They painted it by brush completly, over rust and paint with just wire brushing it before hand painting it. Within a short while (six months or so) I could not even get the paint off from the rust area with a knife, but on nearly all of the rest of the truck the paint formed large bubbles (over six inches across) and just peeled the orignal paint off right down to the orignal shiny sheet metal. Is there certain types of paint that these 'rust paints' can react with to cause this? Or, was it just that it happens to be a wierd paint that they used at the factory because of it being a war time truck? (The paint on the truck had no bubbles before putting on the Zero Rust.) Do I need to take these old rigs all the way to solid bare metal? Or, is Rustoleum different then Zero Rust?