Irwin Unibit 1/4 to 1-3/8 in. x 6 in. L High Speed Steel Step Drill Bit 1 pc.The Irwin unibit high speed steel fractional self starting step drill 5, 1 4 inch 1 3 8 inch is ideal for drilling clean, smooth holes in mild steel, copper, bass, aluminum, Plexiglass, wood and laminate. Crafted of high speed steel, it has a speed point tip that guarantees fast starts and a single flute cutting edge for drilling true, round holes with a precise step control for multiple sizes. Hole sizes are permanently laser etched on the inside of