DEWALT DW1646 5-1/2-Inch Selfeed Bit Extension Aggressive spur provides fast material penetraion Optimized cutting geometry provides longer bit life Open tooth design allows for more resharpenings 7/16" Ball groove shank for quick change applications Aggressive spur provides fast material penetraion Optimized cutting geometry provides longer bit life Open tooth design allows for more resharpenings 7/16-inch ball groove shank for quick change applications