It is a heavy duty screwdriver that different bits can be inserted into. One places the bit into the screw and WHACKS the butt end with a BFH! This motion causes the bit to turn about 30* while under the impact of the hammer.
This does two things... First the screw head is depressed into the material it is holding.. which can in itself loosen it. Then it also UNSCREWS the screw 30* while under the strain of the hammer blow.
I rerely use mine but when I have needed it the thing has always come thru for me.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />