For #50 National Standard Taper Spindle Milling Machines. Arbors are made of top quality one piece forgings. Carefully heat treated and surfaces ground with extremely narrow tolerances assure a rigid setup and accurate machining operations. All threads are ground. Arbors are equipped with assorted solid spacers and necessary running bushings with standard keyways and threaded arbor nut. Type A arbors are provided with end pilots 23/32 x 1-3/4".