Impact Wrenches Information

Pneumatic impact wrenchImpact wrenches use stored rotational kinetic energy to deliver a large amount of torque but over a fraction of a rotation. Applications for impact wrenches include building and construction projects, tightening nuts and bolts requiring high amounts of tightening torque such as in automotive and heavy equipment maintenance, and product assembly. Impact wrenches are usually handheld but may be mounted on articulating arms for factory assembly applications. They are also known as impactors, air wrenchs, air guns, rattle guns, or torque guns.


The primary function of an impact wrench is to deliver high torque to nuts and bolts. They operate via a spring-operated hammer that temporarily disconnects from the output, allowing it to spin as fast as it can. This spinning allows the hammer to store its maximum kinetic energy. The spring forces the hammer down, where it impacts the output anvil and delivers all the stored energy in a very short time for maximum power. This process is repeated to rotate the output shaft.




Impact wrenches have two distinctive configurations. The pistol grip configuration involves a grip that is roughly perpendicular to the driving direction. By contrast the inline grip is held with one or both hands on grips that run parallel to driving direction. Inline impact wrenches allow a user to apply more force in the driving direction while driving the bolt, nut, or screw.




There are multiples types of impact wrenches.

   Fist-grip impact wrench

  • Air-operated: Air-operated impact wrenches are the most common in the industry. The rotational force is provided by an air motor and compressed air.
  • Hydraulic: Hydraulic operated impact wrenches use hydraulic fluid and a hydraulic motor to provide the rotational force.
  • Electric: Electric impact wrenches have become increasingly common with cordless power tools. Electric impact drivers are ideal for smaller uses but more torque and speed can be obtained from air-operated impact wrenches.



The follow specifications determine the functionality of an impact wrench.


  • Output torque: Amount of torque generated at the output shaft.
  • Drive size: The size of the socket drive on the impact wrench.
  • Impacts per second: The number of times the impact hammer hits the anvil causing rotational motion in the output shaft.
  • Input pressure: The fluid pressure at the input of the impact wrench. The input pressure only applies to pneumatic or hydraulic operated impact wrenches.

Images credit: