Not sure what the problem, or your question is. A hub is used to hold the piece on the rotary axis of a mill. And thus depends on the fixture used. I have three different fixtures I use, depending on the job.

There are plugins that draw spoked hubs for rings, but it is usually faster just to draw them out. Or copy one over from another model.

For jewelry related CAD, CAM or CNC questions check out the 3dcadjewelry.com forum.

Nice ring, btw! ZBrush ?