Atlas Craftsman Cross Slide Lead Screw for 10" Metal Lathe. This unit came out of a QC54 lathe built about 1945. Please note, like many of these used lead screws,  this screw has some obvious wear in the threads (see photos) and while it is fully functional it will most likely have some backlash due to wear. Overall this screw is 12.5" long with a 1/2"-10TPI left hand thread. Part number is probably a 10F-36 but I cannot say for certain.