Door Mirror Hog Rings?

[lightflow 59 1 Cars]

I just re-placed my external mirrors and internal mirror adjuster plates with new (including making new foam inserts).

 

The holes for the three plastic adjuster plate pins need some sort of hog ring or plug and all but one of mine have a metal insert which I can't easily identify and don't want to remove. On the driver's side I am missing one (it's not a real problem as everything still sits ok as two of the others are present).

 

Service box shows a part which is NFP - seems to be a "hog ring".

 

Any idea what this should be or look like - or indeed suggestions on where or how I fashion a replacement insert?. I should post a pic, but of course it's all covered up now!