Review on Pack of 100pcs uxcell M3x5mm(L)-5.4mm(OD) Metric Threaded Brass Knurl Round Insert Nuts for Enhanced SEO by Nick Granner

Used to avoid seizing M3 nut in 3D printing. That way I don't have to worry about the nut falling off or getting lost because it's fused to the part. You'll need to poke something into the threads to keep the plastic from melting in the middle. I use some long M3 screws but you may prefer to use short set screws. Or maybe you want to scrape melted plastic off the threads of an installed nut. I don't know and I'm not your mother - you can do whatever you want.