|The heads of screws can be oval, flat or round, and each style has a specific purpose for perfect appearance and seating.|
Flat heads can be countersunk or rest flush with the surface.
Oval heads allow for countersinking, but the head protrudes a bit.
Round-headed screws sit on top of the material and are easy to remove.
Some screw types include the wood screw which will make a stronger joining than a nail, or for when other materials must be fastened to wood. A wood screw is tapered to draw the wood together as the screw is inserted.
Sheet metal screws can also be used to join metal to wood, as well as metal to metal, plastic, or other materials. Most sheet metal screws are threaded the entire length from the point to the head, and the threads tend to be sharper than those of wood screws.
Use a machine screw for joining metal parts, such as hinges to metal door jambs. Machine screws are usually inserted into pre-threaded holes and are sometimes used with washers and nuts.
Square-headed bolts with screw heads are called lag screws. They are for heavy holding and are driven in with a wrench rather than a screwdriver.
When choosing screw length the screw should penetrate two-thirds of the combined thickness of the materials being joined. To avoid corrosion you should consider the moisture conditions and the makeup of the materials being fastened. The use of galvanized or other rust-resistant screws may be necessary where rust could be a problem.
Screw Driving Tips
1. Use soap or wax on the screw for easier installation.
2. Hold your work in a vise or clamp when inserting a screw whenever possible. Keep your hands and other body parts away from the tip of the driver if you can’t use a vise.
3. Removing a screw with a damaged slot can be done by taking a hacksaw blade and sawing another slot if the head is exposed enough.
4. Drill a pilot hole before driving a screw. It can be especially crucial with hardwoods or when driving a screw near the end of the board. If you are working with screws of larger diameter, a pilot hole about the same diameter as the shank of the screw should be drilled into the wood to one-third the depth of the length of the screw.
5. Try to keep the screwdriver in line with the screw shank to avoid damaging the screw slot and pushing the screw out of line.