Kester OR421 is a high activity, water-soluble, cored wire flux that is heat stable and exhibits excellent wetting capabilities with less odor. - Kester OR421 is a high activity, water-soluble, cored wire flux. The OR421 is more heat stable, exhibits better wetting capabilities and has less odor than competitive products. The residues left by OR421 are near neutral pH and therefore also less corrosive. The OR421 is classified as ORH1 per J-STD-004. OR421 cored solder wire can be utilized with an open torch or a soldering iron. OR421 will solder copper as well as more difficult to solder materials such as brass and nickel. OR421 can be used on pipes or tubing for applications such as refrigeration coils and heat exchangers. The heat stability of OR421 makes it ideal for high temperature alloys such as Sn95Sb5, Sn63Pb37 and K100LD.