The two gas tubes carry the gases to the tip, via the ____.

The correct choice is mixing chambers, as they play a crucial role in combining the different gases before they reach the tip of the torch. When using oxy-acetylene or similar gas setups for brazing, the mixing chamber ensures that the gases are properly blended in the right proportions to create an effective and efficient flame for the brazing process. This is important because the quality of the flame directly affects the heating and melting of the filler material, leading to strong and durable joints.

In contrast, mixing valves are generally used to control gas flow and pressure but do not specifically refer to the physical space where the gases are combined before combustion. Gas regulators maintain the pressure of gases supplied from the source but do not mix them. Fitting connectors serve as attachment points for various components of the gas delivery system but do not facilitate the mixture of gases. Therefore, mixing chambers are essential for ensuring the correct mixture reaches the torch tip for optimal brazing results.