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" The cordless drill/driver is by far the most popular portable power tool of all time, and it&amp;#039;s not going to lose that title anytime soon. However, cordless drills are beginning to lose ground to a relatively new type of cordless tool, the impact driver. That&amp;#039;s got do-it-yourselfers everywhere asking questions: What&amp;#039;s the difference between a drill/driver and an impact driver? How does an impact driver work? And if I own a drill/driver, why would I need an impact driver?  A cordless drill/driver is a versatile tool that&amp;#039;s designed to drill holes and drive screws. Its keyless chuck accepts a wide variety of round- and hex-shank drill bits and screw-driving bits, as well as hole saws, rotary sanders, wire-wheel brushes, and other accessories. All cordless drill/drivers are also equipped with a slip clutch that allows you to adjust the amount of torque for precise, consistent screwdriving. An impact driver looks similar to a drill/driver but for one noticeable distinction\u2014instead of a keyless chuck, it has a collet that accepts hex-shanked driver bits. This tool is specially engineered to do one job: drive screws, which it does faster and easier than any other tool. Impact drivers can drive long, large fasteners\u2014including fat lag screws\u2014that would stall the very best drill/driver.  The impact driver uses both bit rotation and concussive blows to power-drive screws through the thickest, densest woods. The result of this combo is raw, unadulterated power. In fact, impact drivers typically deliver two to three times more turning force (torque) than the average drill/driver. How powerful? During a recent Popular Mechanics tool test, one 18-volt impact driver drove an astonishing 138 3-inch lag screws on a single charge. Despite its brute strength, an impact driver is easy and comfortable to use because the concussive action transfers much of that high-energy torque directly to the screw, not to your wrist or forearm. (An impact driver does not have a slip clutch, but the concussive action allows you to drive screws with great control and precision.)  So, if you&amp;#039;re planning projects that require driving a ton of screws, or a lot of very large or long screws, then consider an impact driver. For example, impact drivers are ideal for building decks, installing tile backer board, and screwing down plywood subfloors. If you&amp;#039;re not planning to work on such projects, you might want to stick with the versatility of the cordless drill/driver. However, the gap between these two useful tools might be closing: Some manufacturers now offer drill chucks and other hole-drilling accessories for use in an impact driver. "^^<http://www.w3.org/2001/XMLSchema#string>
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