Angle impact drivers have a low profile head to allow work in confined spaces. They have an internal hex chuck to fit hexagonal screwdriver bits. They are used when an additional impacting force is required to drive the screw home. The internal hex collet has a spring loaded pull back sleeve for insertion & ejection of the bit. A ball bearing retains the socket which has a recess for this purpose.
**Battery words** Additionally there is often a choice between single, 2 or 3 speed gears. Most professional impact drivers have a variable speed function.