I've spent much time searching. Can someone tell me what this bit is used for? Here are photos:
Every thread I chase returns to only one item, currently listed on eBay as a Roberts Company 3 bit fly cutter with pilot. The one on eBay has a solid rod in place of the drill bit, but that's trivial.
All indications are that it's designed to cut holes in metal.
The one in the photo may have a taper, allowing it to be inserted directly into a matching spindle.