This backing plate....
2-3/4 Hook & Loop Backing Plate
and this adaptor so it'll work with the PC...
D.A Adapter 5/8" X 11
I do disagree about the bigger pads for finishing... Remember that even when you are using a finishing polish, your DA has *alot* of work to do. Finishing polishes have to work every bit as hard as medium polishes and compounds do to do their work. Using a smaller four inch pad, even for finishing, will give you better results on the PC than bigger pads.