The primary vs secondary selection requires knowledge of how this part mates and how it needs to be fixtured for fab & inspection
I would select the stem OD as your primary since it's the easiest to chuck and most likely is the mating surface (unless it's the stem ID).
The base of the stem is a candidate for secondary, but since there's a cross hole in the stem that appears to be indexed to the sphere grooves, then this hole should be a datum so the grooves can be referenced and held relative to the cross hole.
The base can be secondary and the cross hole tertiary.
For a position of part & assembly ignorance, this is what I'd lean toward.
PS: By the by, you may want to edit your post to indicate dimxpert autodim and not the regular aoutodim, if I'm understanding correctly.
Kevin, thanks for the response.
When you say I should select the OD of the stem and cross hole, does this mean it's possible to select a non-planar/circular/spherical datum reference?