Screws are driven into wood (in holes previously made by a bradawl or gimlet one size smaller) by means of a screw-driver or turnscrew, shown in Fig. 449. This tool consists of a steel blade tapering to a blunt edge at the working end, and fixed by a tang in a wooden handle at the other. The shape and size of both blade and handle depend on the sizes of the screws and the positions in which they are placed, cabinet screw-drivers for instance being long and light to reach into deep work. Screws hold three times as firmly as nails without risk of splitting the wood, and may be withdrawn without suffering or causing any injury. They are sunk below the surface when necessary by means of a tool called a countersink, described on p. 248. The screw-driver blade fitted to the brace and bits (p. 247) is the quickest way of using the tool.