What distinguishes AN fittings from AC fittings?

The distinction between AN fittings and AC fittings primarily lies in several structural features, which include sleeve length, thread pitch, and the presence of a shoulder.

AN fittings are designed with a specific type of shoulder that aids in creating a more secure seal when paired with the corresponding hose and fitting. This feature is integral to their use in high-pressure applications often found in aviation. Additionally, the length of the sleeve and the thread pitch are standardized for AN fittings, which ensures consistency and reliability under operational conditions.

In contrast, AC fittings do not adhere to the same standards as AN fittings and may vary in these design characteristics. The differences in thread pitch can lead to incompatibility issues when trying to connect AN and AC fittings. The variations in sleeve length ensure that when using AN fittings, the correct alignment and connection can be achieved, contributing to safe and effective operation.

Thus, the combination of these features—sleeve length, thread pitch, and the presence of a shoulder—provides a clear differentiation between AN and AC fittings, making option C the correct choice.