Flat-head screw and round-head screws are both used frequently in woodworking and general home repair projects. Each screw is either made with a thread that is designed for either wood or metal. Furthermore, the head of both these kinds of screws are designed to receive either a straight-edged or a Phillips screwdriver. And some screws come with specially designed heads that can accommodate either type of screwdriver. After all these options then there comes the matter of when and where you would use a flat-head or a round-head screw.
The flat-head screw is the woodworker's friend, for he will use this type of screw almost exclusively to hold together all sorts of cabinets, bookcases, stair threads, tables, benches and a host of other items. Usually a cone-shaped depression is made with a countersink tool to hold the head of the screw; and once put in place and tightened the head of the screw is covered with wood putty, sanded down and coated with a wood finish just like the rest of the woodworking project. Flat-head screws also get used in such general construction tasks as hanging drywall, mounting door hinges, mounting cabinets and installing tabletops.
Round-head screws have a much more limited use in the building trades than flat-heads. Also note that round-head is a bit of a misnomer here, for the underside of the screw is flat. This is a very important feature of the screw, for this flat bottom side gives the screw its holding and binding power. This screw is more commonly used with machinery, but you will usually find flat-head screws holding book shelf and lighting tracts to the wall or ceiling. They are also used in lighting fixtures and electrical outlets as well as holding hand rails, towel racks and toilet paper holders to the wall.