Air Powered Die Grinder. I just hooked it up to my compressor and it 'free wheeled' without any performance issues noted. See video for grinder in operation. Straight w/ Rear Exhaust. Blue Point Tools.

Brand: Blue Point
Type: Straight Die Grinder
Grip: Palm
Manufacturer Part Number: AT100A AT100 AT-100 AT 100
Air Inlet Size: Adaptor Not included
Set or Single Item: Single Item
Maximum Speed(RPM): 22000