It is just a form of threaded insert. There's two kinds: a single is built to sort a bulge to the back again aspect on the panel as being a screw is tightened in its threads. Another is likewise drawn in employing a screw, but is drawn to the sleeve https://ar15muzzlebrake31963.blogolize.com/the-greatest-guide-to-threaded-inserts-for-plastics-66274200