Hammer drills are more costly than normal drills because they have more moving parts and must be more robust. Unless you know you'll be drilling through strong material, a standard drill is typically just as effective and far less expensive. The main advantage of the hammer drill is its ability to drive multiple sizes of screw. Most drivers can only handle one size thread per bit, so if you need to drive two different sizes of screw, you will need two separate tools. A hammer drill can simultaneously drive multiple sizes of screw due to its use of a hammer mechanism instead of a motor to drive the tool. In addition to being able to drive multiple sizes of screw, hammer drills are also superior when drilling into hard materials such as concrete or steel. Since they use a mechanical advantage created by a heavy drill head instead of an electric motor, hammer drills are not as susceptible to power failures as other types of drills. Furthermore, since hammer drills use a hammer mechanism instead of an electric motor, they cannot be used in an area where electrical power is unavailable for some reason. For example, if your vehicle has no battery charge and you need to drill into cement to attach a gas tank filler tube, you would be unable to use a conventional drill.