This style of Threaded
Hole Location Gage is made similar to the Solid
Threaded Hole Location Gage except that the threaded portion
of the Threaded Hole Location Gage is tapered. The taper is designed
so that the small end is the lower limit of the thread tolerance
and the large end is the upper limit of the thread tolerance. Taper Threaded Hole Location Gages are used where the surface into which the thread is installed is not perpendicular and square to the centerline of the screw thread. As
the Tapered Threaded Hole Location Gage is screwed into the internal
threaded hole, the thread eventually binds up and locks in place.
I can see where this would be quite accurate. There might be some
tilt because the taper is binding against a helical surface. I expect
the variation to be minimal, if at all existent.