Duffel coat fastener (6)
I believe the answer is:
toggle
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">duffel coat 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 toggle that I've seen before include "Wooden pin" , "Coat fastener; computer switch" , "Fastener; type of switch" , "Fastening eg for Paddington's coat" , "Type of fastening - on/off key" .)