Collar fastener
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">collar fastener</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for stud that I've seen before include "Place of breeding" , "Ladies' man?" , "Group of horses for breeding" , "Football boot peg" , "Bolt" .)