Master Mechanic, #13, 3-1/2", Black Oxide, Wire Gauge Number Drill Bit, Jobber Length, Straight Shank, 135 Split Point Eliminates Walking & Provides Quick Starting, Surface Treated With Black Oxide Finish For Abrasion Resistance & Improved Chip Flow, Designed For Precision Hole Sizing Such As Tapping Threaded Holes, Wire Gauge Diameters Fall Between Fractional Sizes For Most Precise Hole Sizes, Taps Through Sizes 1/4-28 Require The Use Of Wire Gauge Bits, Carded.