Yep, right angle drive, Nope, not a die grinder...
typical 4-1/2" 13,000rpm angle grinder


Then...
I've found these listed as "mounted points", "mounted cones" and "plugs"
web page

Another option I've long thought of for this purpose would be the "Oops Holesaw Arbor" from Starret. It allows you to use a holesaw as an arbor to enlarge a hole-
starrett

We use both of these systems at work. Many times the stone is used following blowing a hole through a truck frame with a plasma cutter. It makes the hole perfectly clean, and eliminates the chance of the radial cracks.