Master Mechanic, #18 3-1/4" M7 Black Oxide, Wire Gauge Drill Bit, Jobber Length, Straight Shank, 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, 135 Split Point Eliminates "Walking" & Provides Quick Starting, Surface Treated With A Black Oxide Finish For Abrasion Resistance & Improved Chip Flow, Carded.