The reinforced ones are a bit thicker, and brown. They’ve got a
woven mesh of fiberglass inside the disk. (or rather, the abrasive
is formed around the fiberglass mesh.) Either way, you can see the
grid pattern of the mesh within the disk. The mesh keeps them from
blowing up every time you glance at them.
I used to get my large ones (for sprue chopping) from a local hobby
store. Apparently the railroaders use them. (2" disk.) About .040"
thick, but I was just chopping sprues, so I didn’t care.
There are smaller ones, for jewelry uses.
Otto Frei has some (but they’re black) (and expensive) (but then
again, so were the hobby store ones) They’re calling them “extra
strong separating disks” They’re normal sized. (7/8" OD)
Rio has the big fiberglass ones I remember, as
"fiberglass-reinforced"cut off wheels. at 1.5" OD, by .040" thick.
Also not nearly as cheap as the normal ones, but vastly less likely
to shatter. So it evens out.