With a built-in hammer, this impact driver actually hammers at the screw or bolt while tightening it, giving it substantial power to easily tighten the thickest screws or hardest bolts. With the aim of developing the "World's No. 1 Impact Driver", we visited countless construction sites and discovered various problems there. One problem was that carpenters had two drivers with them, a small and a large one. For heavy work, a 100V type was used but it was large and unsuited to work in confined areas, not to mention the fact that it was exhausting to use. For light work, a smaller, rechargeable type was used, but it obviously lacked power and couldn't be used for heavy work. This new product combines both functions, making it an indispensable power tool for professional housing construction engineers and workers.