What tool is used to deburr the interior surfaces of each hole?

Using a flat file is the most appropriate choice for deburring the interior surfaces of each hole. When drilling or machining operations are performed, the resulting holes may have sharp edges or burrs—small fragments of material that can interfere with assembly and functionality.

A flat file allows for precision control over the deburring process, making it effective for smoothing out these sharp edges inside holes. It can reach into the interior surfaces and provide a smooth finish without removing excessive material. This is crucial in aerospace assembly, where tolerances are tight and any imperfections could lead to issues in assembly or performance.

Other tools, while useful for different purposes, do not offer the same level of control for this specific task. For instance, a rivet gun is used for creating structural joints but is not designed for deburring. A drill press is primarily a drilling tool, suitable for making holes, while a pneumatic sander is more effective on flat surfaces rather than interior edges of holes. Hence, a flat file is the best tool for this application.