Ask someone on a busy site what tool is attached to their belt and the answer is almost always "impact driver." Ask them to change a wheel on the van and they will probably reach for something completely different. That second tool is an impact wrench, and while the names sound similar, the jobs they do are different enough that using the wrong one wastes time and risks damaging the work.
Milwaukee's UK range covers both categories in depth, and the brand keeps appearing in research because it is one of the most widely used fastening platforms on UK sites. This guide uses Milwaukee's range as a reference point but the principles apply regardless of the battery platform you're on.
What an impact driver does
An impact driver drives screws. That is the job it was built for. It uses a 1/4-inch hex chuck that accepts screwdriver bits: Phillips, Pozidriv, Torx, square drive. The combination of rotation and short, sharp impacts -- hundreds of times per minute -- lets it drive long screws into dense timber without pre-drilling, and without the tool trying to twist out of your hand in the process.
Think of it like cracking open a jar. Pure rotation often doesn't work. A short knock, then twist, does. That is broadly what the impact mechanism provides for the driver.
Milwaukee's M18 FUEL Impact Driver delivers up to 300 Nm of torque. To put that in terms most people will recognise, 300 Nm is roughly the torque required to tighten a car wheel nut to a typical specification. Applied to a 150mm structural screw going into a timber frame, that is more than enough power without pre-drilling in most softwoods.
The 1/4-inch hex chuck cannot accept standard socket sets or spanner sockets. It accepts hex-shank bit holders and some specialist inserts, but it is not designed for fastening bolts, wheel nuts or large hexagonal fasteners.
What an impact wrench does
An impact wrench is designed for bolts, nuts and large hexagonal fixings. Its square drive takes sockets, not screwdriver bits. The most common sizes in UK trade use are 1/2-inch square drive, found on most mid-range impact wrenches, and 3/4-inch square drive on heavy-duty models used in plant maintenance and tyre work.
Where an impact driver delivers its force in a rotational direction only, an impact wrench applies repeated high-torque hammer blows in the direction of the bolt rotation. The result is a tool that can loosen or tighten a rusted wheel nut, a structural bolt, or a large M16 fixing in scaffold tube in seconds.
Milwaukee's M18 FUEL Impact Wrench range covers two drive sizes. The 1/2-inch compact model suits general building and maintenance work: scaffold tube fittings, structural bolt tightening, plant maintenance, wheel changes. The 3/4-inch friction ring model is the heavy-duty option, intended for HGV wheels, large plant and steel frame connection bolts. The friction ring design allows sockets to be released without the tool's release collar, which speeds up socket changes on repetitive work.
To use the wheel nut example again: a 1/2-inch impact wrench set to a realistic torque range can tighten wheel nuts to around 130 Nm, which covers most passenger and light commercial vehicle wheels. For HGV wheel nuts specified at 500 to 700 Nm, you need the 3/4-inch model.
The key differences at a glance
Chuck type: Impact driver uses 1/4-inch hex. Impact wrench uses square drive (typically 1/2-inch or 3/4-inch).
What it fastens: Driver takes screwdriver bits. Wrench takes sockets.
Typical torque range: M18 FUEL Impact Driver up to 300 Nm. M18 FUEL 1/2-inch Impact Wrench up to 813 Nm. M18 FUEL 3/4-inch Impact Wrench up to 1,627 Nm.
Typical applications:
- Driver: structural screws, decking, timber frame, drywall, long chipboard screws, sheet materials.
- Wrench: wheel nuts, scaffold fittings, structural bolts, M12 and above hex fixings, plant maintenance.
Can I use an impact driver to tighten bolts?
With the right adaptor, yes, for light-duty bolts. A 1/4-inch hex to 1/2-inch square adaptor lets you use sockets in an impact driver. For small bolts on light frames or furniture fixings, this works fine. For anything above M8 or M10, or any fixing with a specified torque, this approach is not reliable. Impact drivers are not calibrated for torque and the 1/4-inch hex adaptor is not designed to withstand the shear forces involved in heavy bolt fastening. Use the right tool for the job.
Milwaukee's fastening range in context
Milwaukee structures its cordless fastening tools around the M18 platform, with M12 compact options for light-duty and confined-space work.
M12 FUEL Impact Driver: Compact, lighter than the M18, useful for working in tight spots or overhead. Torque is lower, but for most interior finishing and light trade work the M12 is quick and easy on the wrist over a long shift.
M18 FUEL Impact Driver: The main-line trade driver. Available in standard and compact (Surge) versions. The Surge uses a hydraulic mechanism instead of a mechanical impact, which makes it quieter and produces less vibration, which matters when driving hundreds of screws per day.
M18 FUEL Right Angle Impact Driver: The impact driver head rotates 90 degrees, allowing screw driving in confined spaces: inside joinery units, in stud frames, or between joists where a standard driver cannot fit.
M18 FUEL 1/2-inch Impact Wrench (4-Mode): Four output settings from low to 813 Nm maximum. Friction ring socket release. Compact enough for most general site work.
M18 FUEL 3/4-inch High Torque Impact Wrench: The heavy-duty option. Suited to structural steelwork connections, HGV wheel maintenance and plant/machinery fixings.
All of these use the same M18 batteries, so if your site already runs on Milwaukee M18 REDLITHIUM packs, adding an impact wrench to the kit does not require a new battery ecosystem.
Which tool should I buy if I can only buy one?
For most UK building and joinery trades, the impact driver comes first. You will use it every day for screws, and the 1/4-inch hex adaptor workaround covers light bolt work. If you're on site regularly driving structural screws by the hundred, the impact driver is the foundation tool.
If you work in plant maintenance, vehicle repairs, scaffold erection, or structural steelwork, the impact wrench earns its place as the primary tool and an impact driver may be secondary or unnecessary for your specific work.
Groundworkers and groundworks contractors often need both: an impact driver for fixing formwork and shuttering, and an impact wrench for plant maintenance and scaffold-adjacent bolt work.