Okay I figured it out. I saw a few other counterbores like this and they are called stub tapers. 1,2,3 or 4. I don't think they are MT stub tapers cause mine doesn't match the dimensions. People are asking big bucks for these on eBay.
Large end: ~ .900"
Small end: ~.869"
Length: ~.863"
The hex is .750" across the flats.