Bronze Round Bar 642 is an aluminumsilicon bronze that offers high strength, excellent corrosion resistance, good fatigue resistance, antigalling properties, and high machinability 642 has the highest machinability rating of any nonleaded bronze, additionally the high aluminum and silicon contents make this one of the lightest bronzes Brazing and most forms of welding are only rated as fair though This material is typically used to make blots, gears, and valves