I second Vince's. I recently obtained an electric random orbital sander/polisher. The sanding pad that came with it was 3" with a 6mm male thread. I bought online a 2" and and "1 disk both with 6mm threads. I bought all the interface pads from Vince! Also Vince's oversized sanding discs 2 2/8 and 1 1/8.
Not to go off-topic, I was thinking about purchasing ROS for a long time but couldn't justify going pneumatic. I knew about the Metabo, but found an electric variable speed unit by accident when I was looking to polish my headlights. Found one for 50 bucks on amazon! Also, I am currently doing a lot of inlay work and this acquisition with the smaller discs works like a charm. The angle drill is a little too aggressive and the detailer is a little slow. The ROS is right in the middle performance-wise and its random pattern leaves almost no sanding marks. ROS is not pushed by the WT vendors and you rarely see it being used in demos in the woodturning community as compared to angle drills but it's got my vote.