How can one differentiate between AN fittings and AC fittings?

AN fittings can be distinguished from AC fittings primarily by the presence of a shoulder on AN fittings. This shoulder is a critical feature that allows for precise assembly and alignment within the aircraft systems. In aviation applications, threading and physical dimensions are paramount for ensuring proper sealing and functionality under pressure, and the shoulder facilitates this by providing a clear stop for the fitting during installation.

The design philosophy for AN fittings emphasizes a high level of safety and reliability, which is why they incorporate this shoulder feature. In contrast, AC fittings lack this specific design element and typically provide less defined alignment for assemblies, thus leading to differences in their application and functionality in aviation systems. Understanding these design characteristics is vital for maintaining the integrity of fluid systems in aircraft.