Prevent counter-clockwise rotating parts from loosening and spinning off. These taps thread holes to mate with left-hand Acme fasteners that secure components like lead screw nuts and linear actuators. They have two sets of chamfered threads: the first for cutting a rough profile and the second for finishing it. They’re only for through holes since the two different threads can damage the workpiece if you reverse the tap. Once done threading, release the tap from the holder and remove it from the other side of the hole. Also known as tandem taps.