4- and 8-inch Magnetic Copper Butt-Weld Backer Set
Product Review (submitted on July 4, 2010):
These consist of a nice piece of heavy copper. They works well on very flat surfaces only. It will not conform to surfaces that are not flat so magnets will not adhere to the workpiece. The magnets are held into hole in the copper by a pressure fit. I got mine so hot that he copper expanded and some of the magnets fell out. When I tried to press them back in the magnets broke into pieces.