The pipe expander is a tool used to ___ the end of the pipe and __ the walls to ensure the correct dimension between the pipe outside and the fitting inside.

The pipe expander is specifically designed to round the end of the pipe and expand the walls to facilitate a proper fit between the pipe and the accompanying fitting. By rounding the end of the pipe, any deformations or irregularities are corrected, ensuring a smooth and consistent diameter. Expanding the walls of the pipe creates the necessary tolerances for the fitting to slide over the end securely, which is crucial for effective brazing and joining processes.

This correct answer highlights the function of the pipe expander in preparing the pipe for connections. Ensuring that the pipe is appropriately rounded and expanded prevents leaks and guarantees structural integrity when the brazing process is performed. Each detail in the process allows for better fitting and improves the overall quality of the brazed connection.