Which rivet listed is a flathead style?

The correct choice for identifying a flathead style rivet is the AN 441. Flathead rivets feature a head that is wider than the shank diameter, which allows them to sit flush with the surface of the material they are fastening, making them ideal for aerodynamic purposes where a smooth surface is required.

In the context of rivet standards, AN 441 specifically denotes a flathead rivet designed for use in applications where a non-countersunk option is not just preferred but required. This is particularly important in aviation applications, where aerodynamic efficiency is critical, and having a head that aligns well with the surface contour is beneficial.

Other rivet options, while they may have their own unique styles and applications, do not fit the criteria for a flathead design. Each rivet type is categorized based on specific characteristics that suit them for particular uses in aircraft assembly and repair.