Part of a spur
I believe the answer is:
rowel
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">part of a spur</span>' is the definition.<br/ ><span class="explanation-format__explanation">('rowel' is part of 'spur')</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for rowel that I've seen before include "piece on Spurs" , "Lower into a spur disc" , "Spur spikes" , "Part of a spur" , "Spur's spiked disc" .)