What is rosin core solder primarily used for?

Rosin core solder is primarily used for electrical connections due to its unique composition and properties. The rosin core creates a flux that helps to clean the surfaces being soldered, promoting better adhesion and conductivity between the metal components. This type of solder is specifically formulated for applications involving electrical wiring and circuit connections, as it prevents oxidation and ensures a strong, reliable joint.

The other options, while relating to different soldering techniques, do not align with the specific purpose of rosin core solder. Overhead, vertical, and horizontal soldering refer to the orientation of the task, which can be applied with various solder types but does not uniquely identify the best use case for rosin core solder. It is essential to recognize that the effective use of rosin core solder is best highlighted in the context of electrical connections, making it the most suitable choice in this scenario.