scotchbrite disks

I would not use the Scotch-Brite discs for paint scuffing. They are designed to be powered with a die grinder which is too fast for paint prep. They work great for old gasket removal and surface oxide cleaning but are not the best product for paint.

For scuffing non-sanding primer prior to coating, I think the Scotch-Brite hand pads are the most appropriate product, used by hand. I use the general purpose maroon pads. They can also be used for scuffing old topcoats and are great in uneven or odd areas. For broad, reasonably flat areas, if you want to use power, use the 6" dia sandpaper discs (400 grit) in a VS random orbital sander running at a fairly slow speed. Or a pneumatic DA sander. For a sanding "filler" primer (also called a surfacer) such power discs (in both 220 and 400 grits) are the best way to go where you can get at the surface easily with the tool. Where you can't, use the 6" discs on a small, flexible hand pad. I have never tried the Scotch-Brite pads for a surfacer. Somehow I don't think they would be the appropriate product.

Here's a neat conversion chart I ran across sometime ago that compares the various available Scotch-Brite hand pads with equivalent sandpaper grits.

Rod