Originally Posted by MnHPVA Guy
BTW in the previous thread referred to by Cyqlist, I mentioned marking one notch and a nearby spoke so you can be sure the ball cup didn't end up 180 degrees from it's original orientation. The other day I repaired a friends FM (same ball cup) and forgot to do so. When we installed the rear wheel there was at least 3/16" of lateral runount. Reinstalled the ball cup and the wheel was true again. It's not a problem most of the time, but its simpler to mark them all than to have to reinstall a few.
This is another advantage of taking the hub apart from the left side, if you have an older hub with a threaded left cup with outside flats that makes this possible (see my picture above). Since the left cup is a single thread there is only one way it can go back together. I don't know why they made them with a double thread on the right side and a single thread on the left.