Type of light bulb fitting (7)
I believe the answer is:
bayonet
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">type of light bulb fitting</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 bayonet that I've seen before include "Knife fixed to the end of a rifle" , "Dagger attached to 26 Across" , "Kind of knife attached to a rifle" , "one's attached to one's rifle - that's sort of fitting" , "Type of light bulb fitting" .)