Large metal beam (6)
I believe the answer is:
girder
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">large metal beam</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 girder that I've seen before include "Steel beam" , "Load-bearing beam" , "Structural member" , "Large metal beam used in building" , "Metal beam used in construction" .)