thumb·screw 
/ˈθʌmˌskru:/ noun
plural thumb·screws /ˈθʌmˌskru:/ noun [count] 1 : a device used in the past to torture people by crushing their thumbs — sometimes used figuratively ▪ The government is tightening/putting the thumbscrews on dissenters. [=the government is putting a lot of pressure on dissenters to stop; the government is treating dissenters very harshly] 2 : a type of screw with a flat-sided head that can be held and turned with your thumb and fingers
