lis2323,
I'm using one (single stack) on a 3/4HP long arm buffer machine and two (220 & 400) single stack on a 1/2hp slow speed Baldor, The slow speed one is my primary. They're sold with 7 sheets of the radial wheels sandwiched into one mandrel arbor.
When I saw Toold_up's post, it got me looking into the leftover box of spare wheels and found a horrendously (comically) bad, waste of money, performer knock off that is wider that I bought on Aliexpress to try out. I checked and that arbor accepts the 3M wheels and was able to stack 12 of the 3M's together.
To be honest, the jury is out on going wider, When I got them several years ago, I was first bummed they were so narrow but finding it actually very useful to help get into all the small nooks and crannies and it really helps avoid hitting spots I don't wants touched like paint......etc. These are more finishing wheels, not the macro mass crud removers like a wire wheel. Thats the nice thing of these wheels, they fill a big gap between buffing and the jump down to all the typical coarser grits.
Here's pics of the 12 layer on the china arbor laying next to a stock & orig. 3M wheel. The crappy china ones in purple (there really bad, total waste till now). Buying the box of 3M replacement wheels on ebay makes a lot of sense if you can find some cheap arbors like my AliExpress.
**EDIT: Here's some oxidized light rust pieces from a Starrett surface gauge, only used the 220 & 400 Radial Bristle wheels, nothing else and maybe 30 seconds - 1 min of wheeling. Look for any texture patterns left by the wheel, it's very light and way better than any Nyalox or Wire wheel. The harder the metal, the finer the finish is.