the hub stock that you put the pilot hole and counterbore into is slid over the steel mandrel that you machined to fit and that is still chucked in the lathe. this mandrel is your work holder. a shrink fit is my preferred way and reasonably easy to do in aluminium mounted on steel. only tool needed is a toaster oven. a tight sliding fit would also be OK but would need to be secured somehow, glue or loctite would do it and either heat or some kind of solvent could be used to debond the parts when done. any perceptible slop between the mandrel and hub means the mandrel is too small and needs to be done again.

the whole idea behind this method is that it guarantees perfect concentricity without the need for any indicating or aligning. swapping a part end for end in a regular 3 jaw chuck there is no way you would come even close no matter how much time you spend indicating the part.

oh, and OD= outside diameter, ID= inside diameter