1976 Dart parts book

Chrysler part number is 6029889.
They may be called clips, retainers or nuts.
Used on many Mopars from 1973 thru the 1980's.
Here's a partial list of the vehicles that used 6029889:
73-76 A bodies and B bodies, Cordoba,New Yorker,Diplomat, Volare, Aspen, Dodge Ramchargers,etc.
Somebody will have some of the retainer clips.