13/16 X 20 AutoPro50 Thread Chaser Spindle Tool Construction and Industrial Construction and Industrial foundations, anchor bolts, lag bolts, etc The best and easiest tool ever made. The greatest time saver, since sliced bread The pro50 Chaseemback tools are made of a 50 Rockwell hardness Wrap around the good threads, chase threads in either direction, up or down Check out the rest......and buy the best. Save time, make money.