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Cordless impact drivers look a lot like driver-drills with 1/4-inch hex collets instead of three-jaw chucks, but appearance is where the similarity ends. These tools provide as much power as you'll ever need from a cordless tool — more than twice as much as a comparably sized driver-drill. Unlike the continuous torque of a regular driver-drill, the output of a cordless impact driver is mechanically converted into an intermittent rotational force (see Figure 1). As a result, there is no noticeable torque reaction at the tool or at the workpiece and, even with all the extra power being delivered, there is little or no damage to the screw heads. With the slightest forward pressure and an easy grip on