You can use any size pad you want a Rotary and yes the hook and loop backing is the same.
Pads come in 2", 3" 4", 6.5", 7.5", and 8.5" sizes generally. The orbital or DA machines use a counter weight that is mounted to the machine and provides balance while the machine is in operation. This counter weight is matched to the size of the backing plate being used on the machine.
If the backing plate is bigger than the counter weight then the machine will be out of balance and be all wobbly when in use. So you'll almost always see 6" backing plates being used or recommended on those types of machines but you can go lower. The counter weight is removable on some machines if you want to change the configuration.
Rotary machines have no counter weight by design. So it doesn't matter what size backing plate you use. They only spin in a circular direction and not in a random orbit.
With that said, I have found that larger sized pads (7" or 8") work well for large flat panels but can be difficult or impossible on smaller panels or panels with many curves.
Also the pads for a Orbital/DA tend to be thicker so you can apply more pressure to them when in use. Those machines need that extra pressure to really perform where as a Rotary doesn't.
Greg
