Have we discussed the Knipex Pliers-Wrench yet? In case you don't know, despite sounding terrible, they're actually the best tool I've ever used for soft alloy headset nuts. Expensive, but everyone who'd tried one raves about theirs.
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Like an adjustable, but it applies force holding the jaws closed as you squeeze, so the size is always exactly right. Any fixed-size wrench has to be a little loose, or else it can't go on the nut (interference fit).
If you have one you'll find yourself using it all the time. No I don't have stock in the company!