Originally Posted by
lhbernhardt
Those expander bolts install right to the top of the steerer (unlike the star-fangled inserts used in metal steerer tubes), so you need a gap between the expander and the top cap.
It's worth saying that you never, ever, never use as star-fangled nut in a carbon fibre steerer tube. I've already saved one poster on BFs from damaging his fork beyond repair with that advice. Expander plugs MUST be used, but even then, you might have to experiment to find a design that will bind properly.