These are somewhat specialized inspections that are used to ascertain an aircraft’s conformity to their Type Certificate before a US Airworthiness Certificate can be issued. An example we saw some years ago was a Piper Cherokee being brought in from Canada. It had originally been built for export to Canada and had a carburetor installed that did not conform to it’s US Type Certificate. This required only the proper model carburetor to be installed to achieve conformance. Another example is the T-42A Beech Baron. These are a military variant of the B55-B Baron that were built under military contract. They cannot be issued a Standard US Airworthiness Certificate unless a specific Beech Modification Kit is installed.