Stillson wrench

[ stil-suh n ]
/ ˈstɪl sən /

Trademark.

a monkey wrench with a pivoted, adjustable jaw that grips pipes, bars, etc., more tightly when pressure is exerted on the handle.

British Dictionary definitions for stillson wrench

Stillson wrench
/ (ˈstɪlsən) /

noun

trademark a large wrench having adjustable jaws that tighten as the pressure on the handle is increased