Looking into crank centre ,the hole appears to be hexagonal,but further in it turns square. To those of you who arn't engineers, I would point out that on a square drive,it is the four flats that drive ,not the corners. Sharp square corners in a drive situation would concentrate the stress at the point of the corner,and eventually cause a failure ( known as a stress raiser ). Normal practice is to undercut the corners ,so that the shape resembles a square with a radius generated from the corner back into the parent metal,it may appear that the corner has been weakened ,but because the stress is "shared " by the surface area of the radius it does not concentrate into a crack. Hope that made sense.
btw. those square tapers were very tight,took a lot of force on the extractor,and the heat gun.