The document discusses threading on a lathe. It describes the basic requirements for thread cutting which are an accurately shaped threading tool and moving the tool longitudinally in relation to the workpiece rotation to determine the thread lead. It then provides a step-by-step process for cutting an external thread on a lathe, including preparing the workpiece, mounting the tool, setting the change gears to achieve the desired thread pitch, and engaging the half nut to start the threading cut. Lathes can be used to cut threads as they provide a versatile and simple method using the carriage and lead screw to relate the tool movement to workpiece rotation.