Thumbscrew

The thumbscrew is an instrument of torture which was used in medieval Europe, notably by the Inquisition. It is a simple vise, sometimes with protruding studs on the interior surfaces. The torture victim's thumbs or fingers were placed in the vise and slowly crushed.

Similar devices were sometimes applied to toes, knees, etc.

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Thumbscrew is also used to refer to a screw with a tall head with ridged sides, intended to be tightened and loosened by hand. They usually have a slot for a flathead screwdriver as well.