What is the primary purpose of a gap inspection shim during assembly work?

The primary purpose of a gap inspection shim during assembly work is to check the flushness of parts being assembled, particularly in relation to rivet heads. During assembly, it is crucial for components to fit together smoothly without any bulges or misalignments; this ensures structural integrity and optimal aerodynamic performance. The gap inspection shim provides a consistent reference point to assess whether the surfaces are flush. This is particularly important for aeronautical structures where airflow, structural load, and material performance can be significantly affected by any imperfections in surface alignment.

While measuring length, aligning components, and enhancing adhesive bonding are important processes in assembly work, they do not specifically address the main role of gap inspection shims, which is focused on ensuring the smooth transition between adjacent parts and confirming that any fastener heads, like rivets, sit correctly against the surface of the material. Proper gap inspection helps prevent issues such as water ingress or material fatigue, which can arise from poor flushness during aircraft assembly.