ITEM NAME:2Pcs/set HSS Spiral Flute Step Core Cone Step Drill Bit 1/4" Hex Shank 4-16mm XX Descriptio n Material: high speed steel Color: Silver Dimensions: total length 122mm, shank diameter 12mm, blade length 98mm Model: 4-16.5mm triangular handle spiral groove Blade diameter: 4-16.5mm (4, 6, 8, 10, 12, 14, 16.5 / 7 steps) Application: Suitable for drilling aluminum, wood and plastic materials. Product List: Step drill *2pcs Tips: 1. Hand drill (550W or more) operation thickness 1-2mmde, hole diameter greater than 14mm, requires bench drill operation (recommended to drill stainless steel hardness of 25 degrees below the workpiece) 2. When drilling operation, water injection and cooling while drilling, effectively extend the service life of the drill. (Recommended drilling speed 250~400) We offer you what you need! 3Pcs HSS Spiral Flute Step Drill Bit Set Cutter Drill Core Cone Step Hole.3Pcs HSS Spiral Flute Step Drill Bit Set Cutter Drill Core Cone Step Hole. Step drill 2pcs. Model: 4-16.5mm triangular handle spiral groove. When drilling operation, water injection and cooling while drilling, effectively extend the service life of the drill.