When importing face parts from other systems they often contain gaps between their faces that can be closed with the Reintersect function. However, these gaps can be very small and difficult to detect. Use the Show Gaps command to reveal any gaps (open edges) that exist between faces.
To show gaps between faces,
1. Click Analysis and then, in the Verify group, click Show Gaps.
Alternatively, select a face part in the viewport and click on the Command Mini Toolbar.
2. Specify the part. Any gaps (open edges) in this part are highlighted.
3. You can use Reintersect Faces to close the gaps.
Show Gaps.