What is the impact function?
Every cordless impact driver has an impact function, which consists of a hammer and anvil mechanism inside the tool which produces rapid bursts of torque to the side of the screwdriver bit; very similar to the way in which a hammer provides bursts of linear force to the head of a nail.
This feature is what makes cordless impact drivers particularly suited to heavy duty screwdriving tasks.
How is the impact function measured?
The power of a cordless impact driver's impact function is measured in 'impacts per minute' and will be presented as a number followed by the letters IPM. This number refers to how many times the hammer strikes the anvil in a minute.
A model that can deliver more impacts per minute should be able to overcome greater resistance when working, and drive screws in at a faster rate.
Most cordless impact drivers can deliver around 3,000 impacts per minute - that’s 50 impacts per second!
For more information, see our section:
When will the tool encounter resistance?
Quite simply, if you're working with tougher materials and larger screws, then you are likely to encounter more resistance when working.
If this is the case, look for a cordless impact driver that can deliver more impacts per minute.
When you use adjust the speed of the chuck using the speed control trigger, you are also adjusting the amount of impacts per minute the cordless impact driver is producing.
The further you pull the trigger, the more impacts per minute the tool will deliver. The more you release the trigger, the fewer impacts per minute the tool will produce. Releasing the trigger completely will stop the tool.