Asahi Rosin Activated Core Wire is made of an alloy of Tin at 60% and Lead at 40%. The diameter of the core is 1.0 mm. It's best/ideal for DIY home projects, circuit boards, repairs on TV/Radio/stereo/ Toys e.t.c. It heats up great and sticks perfectly giving a strong long lasting bond. It melts quickly once your soldering iron is at the right temperature is easily absorbed by the twisted naked wires. Moreover, it contains flux that helps minimize the oxides that tend to form when you have hot metals in contact with the air.