How to choose an impact driver: battery, drive, bolt

To tighten and loosen medium and large bolts (M12 to M24, wheels, steelwork, structures), choose an 18 V cordless impact driver with a ½″ square drive. For small screws and bolts and precision work, the 12 V models with a ¼″ hex drive are enough, being lighter and more compact. If you have a compressor in the workshop and work on large bolts, up to M42 in our collection, you need an air-powered model and a larger square drive. Always check the maximum bolt diameter stated: it is the figure that tells you whether the tool can cope.

The types

• 12 V cordless impact driver. Compact, with a ¼″ hex drive for bits and inserts. Suitable for small screws and bolts, sheet metal, installations and assembly in tight spaces. One example is the M12 FID2 Milwaukee.
• 18 V cordless impact driver. This is the most common type: ½″ square drive for impact sockets, more torque, more run time. It includes the Milwaukee M18 models, such as the M18 FID3, and the DeWalt XR series, such as the compact 3-speed DCF860E2T-QW.
• Multi-speed or multi-mode impact driver. In the data sheets you will find no-load speeds such as 0-1100 / 2100 / 3200 / 3700 rpm: this means you can choose a low setting for small screws and a high one for stubborn bolts.
• Air-powered impact driver. It runs on compressed air, with no battery. It must be supplied with filtered, lubricated air. It is the choice for anyone tightening bolts all day in the workshop or in production.
• Air ratchet. Compact, for reaching nuts in spaces where an ordinary impact driver will not fit.
• Impulse wrench and hydraulic driver. These are names under which some models appear in the catalogue. Check the data sheet of the individual product (power source, drive, torque) before choosing.

In site jargon, "impact" and "impulse" tools are often used as synonyms. In both cases the tool does not drive continuously but delivers a series of rotary blows.

How to choose by job

The features to look at

• Maximum bolt diameter. In the collection it ranges from M12 to M42. Choose a value above the one you normally use, not equal to it.
• Drive. ¼″ hex for bits and inserts; ¼″, ⅜″, ½″ and 1″ square for sockets. The larger square drive is for the larger bolts. Your socket set must have the same drive.
• Voltage. From 7.2 V to 40 V, with Li-Ion batteries. 12 V is for light work, 18-20 V for heavy work, 40 V for the most demanding work.
• No-load speed. From about 1,000 to 3,700 rpm. More modes mean more control on delicate parts.
• Weight. From 0.8 to 7 kg. For overhead work or work at height every 100 g counts.
• Noise. The sound power level LwA ranges from 102 to 110 dB(A), the sound pressure level LpA from 80 to 100 dB(A): these are noisy tools, ear defenders are required.

Common mistakes

• Using it for tightening to a specified torque. An impact tool does not give a precise torque. The bolt is run down almost to the stop and finished with the torque wrench.
• Fitting ordinary chrome sockets. They shatter under the blows. You need impact sockets, in tougher steel.
• Choosing on volts alone. Two 18 V tools can have very different drives, torque and weight.
• Holding the trigger after the bolt is seated. It ruins threads and heads. Release when the part is fully tightened.
• Supplying an air tool with dirty or dry air. The air motor needs filtered, lubricated air, otherwise it wears out early.

Frequently asked questions

12 V or 18 V: which is better?

It depends on the bolt. For small bolts and light, continuous work the 12 V is more convenient. For medium and large bolts, wheels and steelwork, choose the 18 V.

Can I use an impact driver on small screws?

Yes, if you choose a model with adjustable power levels and start from the lowest. Impacts on small screws can break the head or strip the recess.

Do I still need a torque wrench?

Yes, whenever the tightening has a specified torque, as on many flanges and mechanical components. The impact driver brings the bolt close to the end, and the torque wrench finishes it.

Cordless or air-powered?

Cordless gives you more freedom: no hoses, no compressor. Air-powered is lighter for the same power and suited to continuous use, but requires an air line.

You will find all the models in the Impulse Drivers and Impact Wrenches collection: if you are not sure which drive or how much power you need, write to the AMES technicians and ask for a quote or advice.