How to align pivot to the center of a hole I've got a button model, that is supposed to be rotate around the pivot point in the center,

But how to set the pivot point to the exact center is a problem, the center should be further into the hollow area
I know this model is simple and if you create it from a cylinder the pivot is what I want, but I want to know if say I got model from other people and the pivot is not in the center, how can I align it to the center,thanks.
In Edit mode, '2' for edge select then ALT-click on the top edge round the inside of the hole and SHIFT-S &gt; Cursor to Selected.
If you want it half way down the hole, go to Face mode, ALT-Click one of the edges inside the hole to select the ring of inner faces then SHIFT-S &gt; Cursor to Selected again.