What is measured to verify that the correct fastener length was installed?

The correct measure to verify that the correct fastener length has been installed is grip. Grip refers to the thickness of the materials being joined by a fastener, plus any additional thickness that the fastener must accommodate to ensure a secure connection. When determining the appropriate fastener length, it's essential to consider the grip to ensure that the fastener can properly engage with the material and provide the necessary clamping force without being too short or excessively long.

Measuring the grip ensures that the fastener is neither under-installed, which could lead to a weak joint, nor over-installed, which could risk damage to the materials being joined. This concept is especially critical in aerospace applications where the integrity of assemblies is paramount for safety and performance.

While length, diameter, and gap are relevant measurements in various contexts, they do not specifically address the requirements for verifying fastener length in the context of material grip. Length could refer to the overall size of the fastener, diameter pertains to the width of the fastener, and gap might refer to the space between components, but none directly indicate whether the right amount of grip is achieved to maintain a secure joint. This highlights the importance of focusing on grip when determining the adequacy of fastener installation.