Toothed rack (7)
I believe the answer is:
ratchet
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">toothed rack</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for ratchet that I've seen before include "Toothed rack" , "this will stop revolutionary backsliding" , "Bar that fits into the notches of a toothed wheel" , "One-way mechanism" , "Mechanism with a toothed bar or wheel" .)