This hand tool is used to unscrew bolts that may have become rusted into place. One end has a 3/8th inch socket stub over which you fit with the appropriate socket head. You place this over the bolt and then use a hammer/mallet to hit the other end of the cylindrical tool while applying a slight twisting force on the the body of the impact wrench. The perpendicular motion of the hammer is translated (via a system of springs and prawls) into a sudden twisting motion at the head of the troublesome bolt. Since static friction decreases so much when the force is applied over a very short duration —like the time it takes a hammer to smack the end of the impact wrench — bolts that would otherwise require so much force that they might snap off can be easily removed. Very cool tool. Other tool makers make things very similar, but in my experience, the Snap-on version works best.
— Gabriel Pilar
Snap-On Impact Driver
This hand-held Impact Driver is not to be confused with the hundreds of pneumatic and power Impact Drivers which have largely replaced it. For occasional use, this little guy will do — although it takes some skill to keep it on the bolt when you hammer it. I’ve used the Craftman’s brand, which is half the cost of the Snap-On.
Craftsman Impact Driver
Sears item #00947641000