If you are asking what’s a rivnut?

Typically a rivnut is a threaded insert that can be compared somewhat to a rivet in function. They are made to fit tightly into a drilled or punched hole through thin metal, and when using the proper tool a portion of the corrugated area on the outside barrel of the rivnut expands and collapses to lock itself into the hole becoming a captured nut for a bolt to be screwed into.