What type of marking tool should you use when marking fastener locations on any part?

When marking fastener locations on any part, a non-graphite pencil is the appropriate choice due to its precision and the fact that it leaves a clear, easily removable mark. This is particularly important in aerospace applications, where precision is critical, and markings need to be made without compromising the surface of the part or introducing materials that could lead to contamination or corrosion.

Non-graphite pencils utilize a marking material that doesn't leave a significant residue, ensuring that the markings can be easily cleaned off without damage to the part, which is vital for maintaining the integrity of the surfaces involved in assembly. These tools prevent the introduction of graphite, which can conduct electricity or cause other issues in sensitive electronic components or components that require integrity in their surface finish.

In contrast, other options like a ballpoint pen or a permanent marker could leave ink that may be difficult to remove or could interfere with subsequent assembly processes. Sharpies, while they leave bold marks, often use ink that might smudge or react negatively with certain materials used in aerospace applications. Thus, the use of a non-graphite pencil aligns with best practices in aerospace assembly regarding surface treatment and marking methods.