This question would be asked to gauge a candidate's experience with machining operations, which are largely handled on either a milling machine or a lathe. Lathe operations involve securing and rotating the part being worked on and positioning a cutting tool to remove material from the part. Lathes are ideal for cylindrical parts, but they can also be produced on computer-controlled (CNC) milling machines. Another aspect of this question involves the threaded hole, which is created using a tap. A tap is used to create female threads on the inside of parts, and 1/4 -20 (pronounced quarter-twenty) refers to the diameter and pitch of the screw threads.