Heat-set inserts are stock parts that add threads to a part made from a thermoplastic. Since 3D-printing relies on oozing plastic out of nozzles, literally every single 3D-printed material fits ...
Stephan also tried gluing inserts into the parts using resin and CA glue. The resin didn’t cure properly in the opaque parts (6 kg) while CA was comparable to plastic threads, failing at 52 kg.