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1 October 2020

Cordless drill features explained

Confused by combination drills? Stumped by screwdriving mode? Our glossary explains the terms you'll come across when buying a drill.
Drill on wooden bench
Aaron West

There are lots of different uses and modes to consider when buying a drill. Use this guide to learn more about various drill types and features, so you can make sure you buy the right one for you.

Once you know what you’re looking for, head over to our drill reviews to see which models are good enough to be Which? Best Buys.


Amp hours (Ah)

Amp hours, or Ah, is the unit used for the capacity of a battery. Generally speaking, the more Ah a battery has, the longer its charge will last - although this also depends on other factors, including power consumption.

Automatic locking chuck

Most drills lock automatically when the speed control is released, but some manual models require you to slide a switch into the central position to ensure that the bit has been securely attached to the chuck.



A drill bit is simply the drill point, which bores into the surface you're drilling to create the hole. The bit attaches to the drill's chuck, and you can swap it in and out depending on the type of drilling you will be doing. 

Drill bits are available in lots of different sizes and shapes. The size of the chuck will determine the range of bit sizes compatible with your drill.

Brushless motor

Some drills have a brushless motor, which is designed to reduce friction and resistance. Benefits include a higher power-to-weight ratio, higher speed, and greater electronic control. However, drills with brushless motors often cost more than those with standard motors.



The chuck is the hole into which you slot the drill bits, or other accessories such as rotary sanders or wire-wheel brushes. Cordless drill chuck sizes can range from 7mm (1/4 inch) diameter to more than 13mm (1/2 inch).

The drills we've tested have one of two different chuck sizes: 10mm, which is suitable most household jobs, or 13mm. Combination drills tend to have 13mm chucks, which can accomodate larger bits and therefore drill wider holes.

Combination drills

Much like drill-drivers (see below), combination drills are able to drill holes and drive screws. They also have a hammer-drilling mode, which can be used on heavy-duty surfaces such as brick, concrete or paving slabs. The drill hammers into the material as it rotates at speeds up to 30,000rpm.

A combi drill is a good choice if your DIY projects extend to tough masonry, such as garden paving or external walls. For extremely hard surfaces, such as concrete, make sure you use tungsten carbide-tipped hammer-drill bits.



Designed to drill holes and drive screws, drill-drivers are versatile tools that are suitable for the bulk of household DIY. 

They have keyless chucks that will accept a large variety of bits, and a slip clutch that lets you adjust the torque settings for precise, consistent screw driving. This can be useful for constructing flat-pack furniture, for example.



Drills with two gears tend to be best for slow, controlled screwdriving. The first gear gives low speed and high torque, which is what you want for screwdriving. The second gear gives high speed and low torque, which is best for drilling into tough materials. 

To switch between gears, release the trigger and allow the drill to come to a complete stop, then slide the gear switch to the setting you want to use.


Hammer-action mode

Exclusive to combination drills, hammer action uses short, rapid thrusts to ‘hammer’ hard material such as concrete, resulting in quicker drilling with less effort. It's sometimes also called impact drilling mode.


Rotary-drilling mode

A mode all drills use to bore holes. This can be used to drill holes in doors and door frames, in walls for picture hanging, or to put up blinds, curtains and towel rails.


Screwdriving mode

A mode all drills use to screw slowly and effectively. This is done through a slip clutch which allows you to adjust the speed and torque of the drill - to better suit either drilling holes or driving screws.


Tungsten carbide

If you’re working with extremely hard materials, such as concrete, paving slabs or metal, make sure your drill bit is tipped with tungsten carbide. This is approximately twice as strong as steel, and better able to withstand heavy-duty drilling.

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