If you are welding new sheet metal to old sheet metal this is a must buy. During our old car restoration we kept burning holes thru the old sheet metal. We bought this tool and one of us would hold the copper behind the spot to be welded. The copper keeps the weld from blowing a hole thru the metal. Works great. We also used an old piece of copper water pipe that we hammered flat. That gave us a longer reach. Both worked great when wire feed welding. Welding old sheet metal without a copper backing is very difficult.
