The basic Tool Roll?

I realize the thread has grown a bit stale. In reply to Mr. Wong's comment on cheater bars, though.

Many people, even many technicians, don't understand why a cheater bar is bad. So, here's a knowledge biscuit...

It has to do with energy and a material quality called plastic deformation. I'll start with plastic deformation.

Materials which can be stretched are called malleable materials. Most types of steel are malleable. but steels are also Resilient, which means are "springy". So we can think of steel as being able to absorb a certain amount of energy and then spring back to shape. If they have reached their maximum springiness and energy is still applied, they will stretch malleably and NOT return to shape after the force is removed. This point is called plastic deformation.

As plastic deformation increase, strength radically decreases, eventually ending in failure. Think about breaking a paperclip by bending it back and forth. It starts out taking a bit of effort to bend the thing, but the more you work it back and forth, the easier it gets until the paper clip breaks. That's plastic deformation in action.

SO we think of the strength of a normal metal as a curve. The strength remains constant in the resilient range and decreases in plastic deformation. When the strength reaches zero, the material fails.

What does this have to do with cheater bars?

Cheater bars add energy at a constant level. You're applying a torque equal to the length of the bar multiplied by the force you're pulling with. That doesn't change unless the bolt moves ... IF you remain within the resilient region of the object. If you apply too much force and drift into the plastic region, you will break the bolt. You will not be able to relax your pull quickly enough to avoid twisting it off. As the material deforms, the amount of energy required to keep it deforming drops until it fails and you've twisted it right off. If you worked in any of the trades that involve machines, you have done this numerous times.

If you're smart, you got tired of it.

Slugging (impact guns are slugging devices) SAVES material because force is applied is packets. When you whack the tire iron, you're maxing out the force. And then, there's a period of relaxation. This allows the material to "return to zero" all the internal energy is released and you start from square zero again. Engineers call this type of action "impulse" and it's much less likely to cause damage than a constant force approach.

Impact guns aren't magic, they strike quicker than you can by hand. And you can break studs with slugging or an impact gun. It's harder, though.

I could go further but this post is already too long. If you're interested, google it. The deeper you go, the more you'll understand why slugging beats wrenching.

EDIT:
Additionally, when you slug, you adding vibrations, which always helps free the part. Any kind of dynamic loading stresses material boundaries like the gunk that's clogging your threads or the rust film between the bolt head and the part. This is why, even if you MUST use plain torque (cheater bar) it's always a smart idea to take a few whacks at a frozen nut/bolt/stud with a ball peen before you start torqueing on it.