Wheel center (3)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">wheel center</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for hub that I've seen before include "Focus" , "Centre of wheel" , "Centre of activity" , "Centre or axis" , "Focal point of activity" .)