Makes it easy to use your MIG welder to plug small holes in metal. Plug welds are often easier to produce and stronger than spot welds, so many body panels can be attached this way. The copper-alloy swivel back pad eliminates the problem of burn-thru because it absorbs excess heat; also, the weld will not stick to the copper pad. "U"-shaped movable jaw provides even clamping pressure around the spot to be welded.
