When using a gap inspection shim, should it fit under both the manufactured head and the collar of the Hi-Lok?

In the context of using a gap inspection shim with Hi-Lok fasteners, the correct answer is that the shim should not fit under both the manufactured head and the collar. The purpose of the gap inspection shim is to ensure that the fastener is properly installed and that there is an appropriate gap between the parts being joined to prevent issues such as loosening or improper loading.

When the shim fits under both components, it can lead to errors in measurement and might indicate an improper installation or alignment. The intended use of the shim is to assess the gap and ensure that the components are correctly positioned and that the fastener operates as expected. By only allowing the shim to fit under one part, you ensure that any gap measurements are accurate and relevant to the specific application of the Hi-Lok.

Using the shim specifically under the collar or the manufactured head could provide insights into the fitment of those components without causing confusion about the installation integrity. Ensuring the right fit helps maintain the structural integrity and performance of the aircraft assembly.