This is a nice clean Perfected firm joint Screw Adjusting inside caliper with the extra nice fine adjustment feature (the small knurled nut) that uses a screw type adjustment design to move the one side of the caliper in or out slightly for fine feel, or adjustment. The caliper is 12" long, and is in very good working condition, with minor staining and light pitting in a few places, none of the pitting effect precision use of the tool. It is marked "THE L.S. STARRETT CO. ATHOL MASS. U.S.A.". A quality made precision machinist tool, and one of their best models at that!