Flat Bit: These have a central point but a flat cutting edge and look a little like a small spade. A sharp flat bit will rapidly cut a holes. They are available in sizes of 6mm up to 38mm. They are suited to drilling large holes, where other bit types get expensive.  They cannot be used to widen existing holes.

It is possible to drill a nice neat hole with flat bits. The kind of flat-bit we refer to above are individual one-piece bits with a decent cutting edge ground on them.

Now replaced by Dewalt Extreme, for even better performance.