Jacobs 14135 44-J9 Tap Chuck with Tap Capacity 1/2-Inch and 0.5-Inch Square Hole Mount Simplify tap changing and provide unmatched accuracy 1/2-Inch sqaure hole Positive-drive chuck jaws always locate square of tap shank to ensure superior performance Simple operation- 1/4 turn of chuck screw to disengage back jaws Tap shank sighting hole for full view of tap square during changeovers