Bolt inserts for fun and profit

These arrived today from Amazon. I’m looking forward to having a go with them. And no, they are not bullets. They are for placing brass inserts into 3D printed plastic. You put them on the end of a soldering iron and heat them up so that the plastic melts around the insert. The inserts have screw threads in them. If I can get this right I can make 3D printed objects which I can screw together properly.

These are the inserts. They take m3 bolts.