Spiral drill bit set with extension. These drills are also called auger drills. Screw drills are designed for machining materials, drilling deep holes without the need to periodically remove the drill bit to remove chips. These drill bits are used for working with wooden surfaces. The length of the drill bit is 165mm and the length of the extension is 300mm. Thus the total length of the drill bit is 465mm. The set comes with 8 drill bits from 10mm to 25mm in hole diameter. The drill bits have a 1\4 inch hexagonal shank. The drill bits are stored in a neat box.