+1 on wrapping them. 754 they are aluminum and are a bugger. I actually abandoned them inside on my bike and clamped them on the clip-on bar.
You'll probably have to re-tap the expander, wrap them with plastic electric tape, then try again. I'd use some blue LocTite on them when re threading inside the bar end. Seems to be more of a problem not with the expander, but the diameter of the bar end which is not "universal" for this type of fixture.