There are four categories of options for configuration of flux-cored solder wire. The formula will be the type of flux inside (core) of the wire. The solder alloy, whether it is leaded or lead-free, is what the wire itself is made of. The outside diameter of the wire is available in the range from 0.010” to 0.125”, but certain diameters may not be available for all formulas or alloys. Finally, the flux percentage by weight is commonly 1.1%, 2.2%, or 3.3%.