What tool is primarily used to edge break the holes in an aerospace assembly?

The open countersink tool is primarily used to edge break the holes in aerospace assemblies because it is specifically designed to create a smooth, beveled edge around drilled holes. This process is critical in aerospace applications, as it not only enhances the aesthetic appeal of the assembly but also helps in preventing stress concentrations that can lead to material fatigue and failure. The tool is used to create a conical depression at the entrance of the hole, which allows for better fitting of rivets or fasteners and ensures that components are assembled securely and correctly.

Using the open countersink tool also helps in performance and safety by reducing the chances of sharp edges that could cause injury or snagging during assembly or maintenance. Overall, the tool's ability to produce a precise finish and improve joint integrity makes it an essential part of the aerospace assembly toolkit.