When attaching rivets, which type is suitable for a 100° countersink?

Flat head rivets are specifically designed to fit into countersunk holes, making them suitable for a 100° countersink. The flat head allows for a smooth surface finish when the rivet is installed; it sits flush with the surface of the material being joined. This characteristic is essential for reducing aerodynamic drag and providing a clean appearance, particularly in applications where the structure may be exposed to airflow, such as in aerospace or automotive industries.

In contrast, round head rivets would protrude from the surface, which is not ideal for applications requiring a flush finish. Cherry rivets, typically used for fast assembly and repairs, do not have the flat head design suitable for countersinking. Lastly, while "100° countersink rivets" might sound relevant, they imply a specific type of rivet designed for such countersinks, but the question focuses on the type of head design that allows accommodation in that particular countersink angle, which is accurately represented by flat head rivets.