How are A, B, D, AD, and DD rivets marked?

The correct choice details the specific markings associated with various rivet types, which is essential for differentiating between them in aircraft construction and repair processes.

A rivets, also known as plain rivets, are unmarked, which indicates they are the basic type without any additional features. B rivets are designated for use in securing structures where some added strength is required, and they have a cross marking to indicate this extra capacity. D rivets are designed for applications where a higher shear strength is necessary, marked with a raised dot to signal this enhanced performance. AD rivets combine features of both A and D types; they have a dimple marking to indicate they are manufactured with aluminum alloy and have a similar strength increase over A rivets. Finally, DD rivets, which are similar to AD rivets but with more improved characteristics, are marked with a double dash.

Understanding these markings is crucial for aircraft maintenance and construction, as using the wrong type of rivet can lead to structural failures and safety issues. The other options do not accurately describe the markings, leading to potential confusion in identifying the appropriate rivet type for specific applications in aviation.