What tool is used to shave the heads of fluid tight rivets?

The tool specifically designed for shaving the heads of fluid tight rivets is the rivet shaver. A rivet shaver is engineered to create a smooth surface on the rivet head that ensures a proper seal and maintains the integrity of the assembly. This is particularly important for fluid tight applications, as any irregularities in the rivet head could lead to leaks.

The design of the rivet shaver allows it to remove material from the rivet head evenly without compromising the strength of the surrounding structure. This tool typically features a cutting mechanism and guides that help maintain the correct angle and depth during the shaving process.

Other tools listed, such as a hexagonal wrench, drill, and deburring tool, serve different purposes. A hexagonal wrench is used for turning hexagonal fasteners, a drill is utilized for creating holes, and a deburring tool is meant for removing burrs from edges or surfaces but does not specifically address the modification of rivet heads in the context of fluid tightness. Therefore, the rivet shaver is the correct answer for ensuring the proper treatment of rivet heads in fluid tight applications.