I looked up rivnuts and they certainly look similar.
They are definitely
not standoffs though. I shall look closer at rivnuts.
also look at nutserts.
Riv-nuts are pop-rivets with a threaded center. Usable through sheet
metal, and into blind holes (very carefully)
Nutserts call for drilling and threading a hole and screwing them in.
I'm assuming that you are talking about threaded inserts in a plastic
piece?