If you're talking about wire to wrap the joints where the music wire cabanes are soldered, I use thin copper wire, about 28 gauge, and wrap a double layer. Use silver solder, stronger than regular tin/lead, but requires more heat. make sure the piano wire is absolutely grease free, clean it with naptha, alcohol, MEK or lacquer thinner, then use 100 grit sandpaper and sand it shiny where the solder joint will be, then wrap the copper, flux well (I like paste better than liquid, it stays better)heat and solder. I think a MAPP gas torch works best.