Best alloy for general copper-copper brazing in the Sil-Fos family. For copper-to-copper joints the phosphorus in the Sil-Fos product serves as the fluxing agent and no separate flux is necessary. For brass applications however, flux is recommended. For use where close fit-ups cannot be maintained Sil-Fos 15 works well to "bridge" gaps. Highest joint ductility of the entire Sil-Fos family to best withstand the stresses inherent in refrigeration applications. Slow flow.