Headset wrenches are expensive, and if you work on many bikes, you can't realistically buy one to fit each headset. I've had to improvise with things like slip-joint pliers. I don't like using pliers where wrenches belong, but it seems to be less of a disaster on big nuts like these compared with smaller ones. Not a disaster at all, really. And maybe my 12" adjustable wrench is a high quality one, because it doesn't slip. Actually, yes, it's at least 20 years old.