An impact driver is a tool that delivers a strong, sudden rotational force and forward thrust. The force can be delivered either by striking with a hammer in the case of manual impact drivers, or mechanically in the case of powered impact drivers. Impact driver bits

It is often used by

mechanic A mechanic is a skilled tradesperson who uses tools to build, maintain, or repair machinery, especially engines. Formerly, the term meant any member of the handicraft trades, but by the early 20th century, it had come to mean one who works w ...

s to loosen larger

screws A screw is an externally helical threaded fastener capable of being tightened or released by a twisting force (torque) to the screw head, head. The most common uses of screws are to hold objects together and there are many forms for a variety ...

, bolts and nuts that are corrosively "frozen" or over-torqued. The direction can also be reversed for situations where screws have to be tightened with torque greater than a

screwdriver A screwdriver is a tool, manual or powered, used for turning screws. Description A typical simple screwdriver has a handle and a shaft, ending in a tip the user puts into the screw head before turning the handle. This form of the screwdriver ...

can reasonably provide.

Manual impact drivers

Manual impact drivers consist of a heavy outer sleeve that surrounds an inner core that is splined to it. The spline is curved so that when the user strikes the outer sleeve with a hammer, its downward force works on the spline to produce turning force on the core and any socket or work bit attached to it. The tool translates the heavy

rotational inertia The moment of inertia, otherwise known as the mass moment of inertia, angular/rotational mass, second moment of mass, or most accurately, rotational inertia, of a rigid body is defined relatively to a rotational axis. It is the ratio between ...

of the sleeve to the lighter core to generate large amounts of torque. At the same time, the striking blow from the hammer forces the impact driver forward into the screw reducing or eliminating cam out. This attribute is beneficial for

Phillips screw Phillips may refer to: Businesses Energy * Chevron Phillips Chemical, American petrochemical firm jointly owned by Chevron Corporation and Phillips 66. * ConocoPhillips, American energy company * Phillips 66, American energy company * Ph ...

s which are prone to cam out. It is also excellent for use with the Robertson square socket head screws that are in common use in

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Powered impact drivers

Typical battery-powered impact drivers are similar to electric drills when used to drive screws or bolts, but additionally have a spring-driven mechanism that applies rotational striking blows once the torque required becomes too great for the motor alone. This should not be confused with the hammer mechanism found on hammer drills, which is a longitudinal blow. Most impact drivers have a handle to make it easier to hold onto. An impact driver is more appropriate than a drill for tightening bolts.

Comparison to an impact wrench

An electric impact driver typically delivers less torque and accepts smaller tool bits than an

impact wrench An impact wrench (also known as an impactor, impact gun, air wrench, air gun, rattle gun, torque gun, windy gun) is a socket wrench power tool designed to deliver high torque output with minimal exertion by the user, by storing energy in a ro ...

. This makes the impact driver more suitable for driving smaller screws in (for example)

construction Construction are processes involved in delivering buildings, infrastructure, industrial facilities, and associated activities through to the end of their life. It typically starts with planning, financing, and design that continues until the a ...

work, while an impact wrench is preferred in situations requiring more torque to drive larger bolts and nuts (such as

lug nut A lug nut or wheel nut is a fastener, specifically a nut (hardware), nut, used to secure a wheel on a vehicle. Typically, lug nuts are found on automobiles, trucks (lorries), and other large vehicles using rubber tires. Design A lug nut is a ...

s).

References

{{Power tools Mechanical hand tools