A composite honeycomb layup cannot be threaded. However, it is necessary to thread screws into composites, so threaded inserts are glued into oversize holes that are drilled through the composite. An insert's threads are strong, so an insert can receive forces from a screw.
The insert distributes the forces from a screw, through the insert, through an epoxy glue, and into the composite. The installation procedure must preclude air bubbles from the epoxy glue. These test samples are sectioned to check for embedded bubbles.

From AstroboticBlogPhotos

From AstroboticBlogPhotos