In article ,
Rick wrote:

They look like washers with wings internally and made of spring
steel, they are designed to slide onto a bar in one direction
only and act as a cheap nut. The seem to be found in mass
produced items.

Radiospares call them "Push-on Retaining Fixings", which
doesn't sound like the name I can't remember.

http://rswww.com 2mm = part number 172-307, up to 7/16"
which is 172-470.

--
Tony Williams.