Heat shrink solder butt connectors are terminals that are used to mate, connect, or terminate a single wire. These terminals provide the ability to solder wire to the terminal, providing a better chance of reliable connectivity. Solder butt connectors can be used in automotive, industrial and other applications that use wire to transfer electrical current. Solder Butt Connectors are adhesive lined with heat shrink sleeving. Just insert stripped cables into the connectors and heat with a hot air gun. This melts the solder and also shrinks the heat shrink tubing sealing the connection. This Kit includes all 3 different sizes: - 10 x Red Heat Shrink Solder Butt Connectors - 0.5mm - 1.5mm. Internal Diameter - 2.7mm - 10 x Blue Heat Shrink Solder Butt Connectors - 1.5mm - 2.5mm. Internal Diameter - 4.5mm - 10 x Yellow Heat Shrink Solder Butt Connectors - 3mm - 6mm. Internal Diameter - 6mm