The Philips head is a common screw and screwdriver. Its design reduces blade slippage from the cross-shaped slot and lends itself to driving with a power bit. The conventional screwdriver has a single blade and is used with screws of matching heads. Battery-powered cordless screwdrivers are now on the market and are a very helpful tool. Screw heads are usually flat oval, or round, and each has a specific purpose for final seating and appearance.
Flat heads are always countersunk or rest flush with the surface.
Oval heads permit countersinking, but the head protrudes somewhat. Round-headed screws rest on top of the material and are easiest to remove. Screw types include the wood screw for when stronger joining than a nail is needed, or for when other materials must be fastened to wood. This screw is tapered to help draw the wood together as the screw is inserted. A sheet metal screw can also be used to fasten metal to wood, as well as metal to metal, plastic, or other materials.