This Oatey 1.7 oz No. 5 Lead-Free Solder Paste Flux is a smooth, non-runny paste that applies easily and spreads evenly. Paste flux cleans and fluxes copper piping to provide uniform solder flow. The self-cleaning formula is good for soft solder applications of copper tube and fittings in plumbing, HVAC, fire sprinkler and other systems. This material is safe for potable water applications.