Bob Engelhardt wrote in
:

Wes wrote:
The drilled hole using a conventional hole is the pilot. The flat
ground one guides on the previous drilled hole and takes out the
drill cusp.

That's just flattening the bottom of a blind hole, that's not
counterboring - where the counterbore is larger than the drill hole.
Or maybe that's called counterboring, too, even though it's a very
special case.

Bob

I think you missed a part of the process involving different size
drills....

Drill the shank hole for fastener, through, blind, tapped, whatever.
Switch to a normal drill of a larger size to clear the head of the
fastener. Drill on the same location to the required 'counterbore' depth.
Then switch to a modified drill with a flatted end to clean the corners of
the counterbore and leave a square shoulder in the hole.