Follow this link to see a cut away view of the impact driver mechanism and an explanation about it. Not good to use with little screws in metal… but nice to use with bolts like Nylex encapsulated nuts, or long self tapping wood screws. Should not damage a screw head like a normal drill will. **Don’t use crap el-cheapo Chinese sockets in an impact driver.. they can shatter and cause serious injury! Buy only impact tool rated sockets.