Ignore the other reviews saying these burn up, or don't work. They are either doing something wrong (like using a torch), or following the instructions.The instructions suggest turning the heat gun up to 700°F. That's too much. I set my heat source to 375°-400°F and had a 100% success rate with the few dozen connectors I used.Some suggestions for use:1. If applying several in a tight area, apply one at a time. These tend to stick together while hot.2. It's possible for a stand of copper to piece through the side as it shrinks. I applied a second layer of heatshrink3. It might not be recommended, but these can be used to connect two wires to a single wire. See attached image, the middle example has white and brown 16 gauge wires connecting to a single 16 gauge blue wire in a 12 gauge (blue) connector.4. You're watching for the solder to go bright during application, but also watch the size of the solder. In the attached image you can see a new connector next to two used ones. That bulge in the center is the solder, as it shrinks you'll know the solder is flowing even if it can't be seen.