A CI class is set as a Principal Class from the Basic Info tab in CI Class Manager by selecting the Principal Class check box. Principal Classes are important because they control which CI classes are treated as primary, operationally meaningful classes in CMDB processes and reference fields. For example, Principal Classes influence which CIs appear in key task fields such as Configuration Item fields on Incident, Change, and other ITSM records. This keeps users from selecting low-level or irrelevant child records when the business process expects a meaningful CI. There is no separate requirement to click a dedicated Principal Class UI Action, and it is not configured through a Yes/No choice list in this scenario. The Basic Info tab exposes the class-level property directly, so checking the Principal Class checkbox is the correct configuration action.