Hollow Spindle Lathes are also commonly referred to as Oil Country Lathes, because they are used for making tool joints, which are probably the most important component in a well drilling operation. Tool joints are the sections of pipe that are screwed together vertically to form the drill string. At the down hole end of the string is the drill head. During drilling a special mud is pumped down through the pipe at high pressure to lubricate the bit and wash the broken rock fragments up to the surface. The mud is then filtered and pumped back down again. If the well hits the oil comes back up through this same pipe. After that the drill string is withdrawn and another set of pipes called a well casing is inserted instead. Oil Country Lathes are used to cut the threads in the ends of these pipes. Because the spindle is hollow one could just project the end of the pipe through the headstock then into the chuck to cut a male thread at the end of a very long pipe. Female joints were made separately and then friction welded onto the pipes. I used to prep the electrics on these too.