Electromagnetism is very inefficient in a small area. That's why the electro-magnet in a junk yard has to be 4 feed wide to lift an old car body. The electro-magnet set up that Ferree's tools marketed in the 1960's was actually a foot pedal operated gizmo that had a rat-a-tat-tat action with the ball actin as a hammer on the inside of the tubing as the outside magnet was turned off and on repeatedly. It did not work in a burnishing action to remove dents. it did not work well enough to become a repair shop staple, and Cliff Ferree decided to discontinue it.