A feature of a special wrench which allows you to turn the handle in one direction to tighten a nut or bolt, but turning it in the opposite direction does nothing but position the handle back where you started and leaves the wrench on the nut or bolt. Likewise you could set the wrench to loosen a nut or bolt. Also see socket wrench .
RATCHET
Meaning of RATCHET in English
English dictionary of automotive terms. Английский словарь автомобильных терминов. 2012