I
hand tool that delivers a strong, sudden torque after being struck by a hammer. In conjunction with toughened socket sets, they are often used by mechanics to loosen larger bolts and nuts that are frozen or over-torqued in place.




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 about 90 degrees and any socket or work bit attached to it. The tool translates the heavy rotational inertia of the sleeve to the lighter core to generate large amounts of torque.

If the tool is powered by a motor instead of by manual striking, it is called an impact wrench instead, and greatly increases the versatility of this type of tool.

K
A keyhole saw (also called a pad saw, alligator saw, jab saw or drywall saw) is a long, narrow saw used for cutting small, often awkward features in various building materials. There are typically two varieties of keyhole saw: the fixed blade type and retractable blade type. The retractable blade variety is usually found to have either a cast iron handle or, less commonly, a wooden handle. The facility to retract the blade to an optimum length serves to prevent unwanted flex to the blade should the full length of the blade be obstructed in some way. In both types the blade is typically secured by one or two holding/thumb screws.
The fixed blade type, often being cheaper to manufacture and purchase (due to fewer parts) is therefore more commonly used in the modern construction trade. With the advance of certain building methods and materials, designs specific to these trades have been developed. One such modification being a sharpened point at the tip of the blade which can be pushed or ‘jabbed’ through soft materials such as drywall without pre-drilling a hole for the blade.
Two power tools serving largely the same function but which work more quickly and with less effort are the jigsaw and spiral saw.