An impact driver is a hand tool that delivers a strong, impact torque after being struck with a hammer. In conjunction with toughened socket sets, they are often used to loosen larger bolts and nuts that are frozen in place or over-torqued. Impact drivers consist of a heavy outer sleeve that surrounds an inner core that is splined to it. When the user strikes the outer sleeve, its downward force works on the spline to turn the core and any socket or work bit attached to it about 90