Dan,
That is the pilot bushing that supports and centers the transmission input shaft. On an automatic car, the crankshaft end has a large hole machined into it. The torque convertor has a round part that fits up to the crank shaft end.
It is impossible to mate up an auto torque convertor if the crankshaft has a pilot bushing in place. The pilot bearing must be removed, Been there and done that.
So, in actuality, the cranks are the same. The pilot bushing is an added in piece for the manual transmission application.
Loren