This six piece set of hard wearing professional flat bits is the best we have ever used. Fast, accurate and clean cutting, they have a self-cutting threaded point to draw them through the work, with two cutting spurs that ensure clean finish. Tip and cutting edges are precision ground for a precise hole size. Suitable for hard and soft woods as well as light building materials, great for boring through joists. They all have a 1/4" hexagonal shank as per DIN 3126-E6.3. The threaded point pulls the bit through so extra care must be taken if used with a power drill. Speed information is stated on the packaging, dependent on the size. Set contains 16mm, 18mm, 20mm, 22mm, 25mm and 32mm plus 152mm extension.