These are the aluminum oxide separating discs. They're 22 by 0.3 millimeters and you can buy them in packs of 10 like these or packs of 100.  They have great cutting ability and what I think is really nice is that they have a maximum speed of 50,000 RPM but they still don't generate a lot of heat. And unlike a lot of the ultra-thin separating discs these don't break easily even when you bend them.  You can tell that they're micro fiber reinforced so they're very durable and economical and you end up saving time because you don't have to change out your disk as often. You can find the aluminum oxide separating disk and other great tools on Stuller.com.