What type of fasteners need to have the heads shaved so that they are completely flush with the surface of the assembly?

The correct answer focuses on the specific function and design of fluid tight rivets. These rivets are intended for applications where a seal is critical to prevent leakage of fluids or gases, such as in fuel tanks or other pressurized systems. To ensure a proper seal and maintain the integrity of the assembly, the heads of fluid tight rivets must be shaved or counter-sunk to be flush with the surrounding surface. This design reduces the risk of potential leak paths that could occur if the rivet head protrudes.

In contrast, other types of rivets, such as solid and structural rivets, may not require a flush finish because their primary function is to provide mechanical strength rather than achieve a fluid-tight seal. While counter-sunk rivets also have a flush design, they are more versatile and used for aerodynamic purposes rather than specifically for fluid-tight applications. However, it is the fluid tight rivets that specifically necessitate shaving the heads for sealing integrity.