How to choose a hex impact driver: torque and battery

The hex-drive impact driver is the right tool for driving long screws, coach screws and small bolts without twisting your wrist. For most site and workshop jobs an 18 V with torque between 160 and 280 Nm is the best choice; for light carpentry, assembly and tight spaces, the compact 10.8-12 V models are enough. Maximum torque in the collection ranges from 56 to 282 Nm, with an impact rate of roughly 3,100 to 4,400 per minute.

The types

• Compact 10.8-12 V: short and light, they fit where others cannot reach. For example the Stanley 10.8 V impact driver.
• 18-20 V: the most common, with more torque and more runtime. Here you will find the DeWalt models, such as the DCF887D2 or the DCF840D2T.
• Brushless: several models are brushless, with less wear and more runtime.
• Different mechanisms: some models use a hydraulic impulse, such as the DCF870E2T.
• Kit or bare tool: you can buy the tool with batteries and charger, or just the bare tool if you already have the batteries.

How to choose by job

The features to look at

• Maximum torque (Nm): in the collection from 56 to 282 Nm. It is the maximum tightening force: high values are for thick screws and bolts, low ones are enough for light assembly.
• No-load speed and impacts per minute: maximum speed between roughly 2,500 and 3,800 rpm and impacts between 3,100 and 4,400. More impacts means faster driving under load.
• Battery voltage and capacity: 10.8, 12, 18 or 20 V; from 1.5 to 5 Ah. Voltage gives power, Ah gives runtime.
• Number of modes: from 1 to 5. More modes allow you to adjust the force, which helps avoid stripping screws.
• Weight and length: from 0.8 to 1.5 kg and from about 100 to 170 mm. For overhead work or tight spaces every gram counts.

A practical tip: if you already work with a battery of a certain brand, look first at the models compatible with it. The bare tool makes sense precisely in this case, because you share the batteries with your other tools. If instead you are starting from scratch, choose a kit with two batteries, so you always have one charged.

The hex drive (the 1/4" type used for bits and inserts) is convenient because changing bits is quick: you push the bit in and it locks. For larger sockets and bolts there are impact wrenches with a square drive, in the dedicated collection.

Common mistakes

• Using ordinary bits: impact drivers need suitable, tougher bits. Ordinary ones shatter.
• Choosing on Nm alone: weight, battery and modes matter too.
• Keeping the trigger pressed once the screw is fully home: the screw strips or breaks. Release as soon as the head seats.
• Using it as a torque wrench: where a precise torque is required, finish tightening with a torque wrench.
• Forgetting the charger: bare-tool versions come without batteries.

Frequently asked questions

How many Nm do I need?

For assembly and light carpentry the lower values in the collection are enough; for larger bolts or heavy use, models above 200 Nm are better.

10.8 V or 18 V?

The 10.8 V is lighter and smaller but has less torque; the 18 V is the most versatile choice.

Do I need the 5 Ah battery?

Only if you work many hours. For occasional use a 1.5-2 Ah one is enough, and lighter.

Can I use ordinary bits?

Better not: you need impact-rated bits, which withstand the impacts without breaking.

You will find all the models in the Impact Drivers (Hex Drive) collection; for advice on the right model, ask the AMES technicians for a quote.