How do thumbscrews work?

Search: thumbscrews

Why: In Even Cowgirls Get the Blues:

That there were ever such instruments as thumbscrews bring tears to your eyes.

Answer: Like a vise!

The victim's fingers were placed inside the instrument and slowly crushed as the torturer turned the handle on top.

These devices have been found across Europe, India, and China.

Source: Medevality, Occasional Hell

The More You Know: If that didn't work, they could always try the head crusher, which was popular during the Spanish Inquisition:

Or the Judas cradle.