It's a kind of threaded insert. There are 2 styles: one is built to type a bulge over the back side of your panel like a screw is tightened in its threads. One other is similarly drawn in using a screw, but is drawn to the sleeve in its place https://emilianoicnvf.tinyblogging.com/indicators-on-custom-cnc-turning-you-should-know-70479472