This is the Low-Temperature Silver-Bearing Solder Model Railroad Electrical Accessory by Ngineering.
A unique blend of 62% tin, 36% lead and 2% silver alloy with a rosin flux core. The .020 diameter is well-suited for reaching tight spaces. Low melting point of 354-372°F 179-189°C makes it ideal for temperature-sensitive components. Includes dispenser tube.