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. It is often used by

mechanic A mechanic is an artisan, skilled tradesperson, or technician who uses tools to build, maintain, or repair machinery, especially cars. Duties Most mechanics specialize in a particular field, such as auto body mechanics, air conditioning and r ...

s to loosen larger

screws A screw and a bolt (see '' Differentiation between bolt and screw'' below) are similar types of fastener typically made of metal and characterized by a helical ridge, called a ''male thread'' (external thread). Screws and bolts are used to fa ...

, bolts and

nut Nut often refers to: * Nut (fruit), fruit composed of a hard shell and a seed, or a collective noun for dry and edible fruits or seeds * Nut (hardware), fastener used with a bolt Nut or Nuts may also refer to: Arts, entertainment, and media Co ...

s 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. 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 has been repla ...

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 mass, second moment of mass, or most accurately, rotational inertia, of a rigid body is a quantity that determines the torque needed for a desired angular acceler ...

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 Cam out (also cam-out or camming out) is a process by which a screwdriver slips out of the head of a screw being driven once the torque required to turn the screw exceeds a certain amount. Repeatedly camming out damages the screw, and possibly also ...

. This attribute is beneficial for Phillips screws which are prone to cam out. It is also excellent for use with the

Robertson Robertson may refer to: People * Robertson (surname) (includes a list of people with this name) * Robertson (given name) * Clan Robertson, a Scottish clan * Robertson, stage name of Belgian magician Étienne-Gaspard Robert (1763–1837) Places ...

square socket head screws that are in common use in

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...

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 shouldn't be confused with the hammer mechanism found on

hammer drill A hammer drill, also known as a percussion drill or impact drill, is a power tool used chiefly for drilling in hard materials. It is a type of rotary drill with an impact mechanism that generates a hammering motion. The percussive mechanism prov ...

s, which is a longitudinal blow.

Compared 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 rota ...

. This makes the impact driver (with its often lesser torque and smaller tool bit) more suited towards driving smaller screws in for example

construction Construction is a general term meaning the art and science to form objects, systems, or organizations,"Construction" def. 1.a. 1.b. and 1.c. ''Oxford English Dictionary'' Second Edition on CD-ROM (v. 4.0) Oxford University Press 2009 and com ...

work, while the more powerful impact wrench is more suitable for driving larger bolts and nuts in heavy mechanical settings, such as

lug nuts 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 ...

References

{{Power tools Mechanical hand tools