What is an Impact Wrench?

Impact wrenches (or rattle guns) are found in the tool chests of mechanics everywhere. They're commonly used for loosening lug nuts from cars and trucks, but they can also be used in any high-torque situation.

Not to be confused with an impact driver, which has a 1/4-inch hex opening, a standard automotive impact wrench can accommodate 1/2-inch sockets of various sizes, including those that can fit a wheel lug, whilst smaller or larger options are available that feature 3/8-inch or 3/4-inch drives respectively.

Impact wrenches have traditionally been as pneumatic-powered tools, similar to the types used on pit road during auto races. The loud whirring sound is their signature and still the most commonly used tool in professional garages. But cordless 18V impact wrenches are now readily available and have the type of power to loosen lug nuts that are roughly tightened at 100 feet of torque. They are also still extremely loud so hearing protection should be worn when using them.

Impact wrenches get their immense torque from a hammering mechanism in the tool that delivers strong concussive blows extremely quickly. When loosening a lug nut you'll notice the socket attached to the impact wrench moving slowly as the lug nut is loosened and then quickly when it's loose. Be cautious when tightening lug nuts using an impact as it's easy to over torque them—which can stretch or even strip the threads.

A standard lug wrench is all that's needed to remove a flat tyre, but if you are looking for speed and convenience (and, let's face it, a chance to pretend like you're in a V8 Supercars pit crew) get an impact wrench.

Tips & Tricks

• Your impact wrench should always be used with impact sockets designed for this purpose.Impact sockets are often distinguished from regular sockets by their thicker walls and flat black appearance, which is a result of their hardening process.
• Always be wary of the power offered by an impact wrench as it is more than enough to snap smaller fasteners, and never rely solely on an impact wrench when using it on torque sensitive fasteners such as wheel nuts. A torque wrench should always be used to apply the final tension to these jobs.
• Due to the high impact nature of the impact wrench, safety glasses should always be worn to prevent eye injury should any component fail under pressure, but when used in the right situations and with a bit of care, an impact wrench will save you plenty of time and effort on every job.