If you can find the service manual for the Commodore SX-64 maybe they will be identified. The boards hold in place with these funny MasterMind-looking pins...
On the right.
These go into a plastic tube that splits open and keeps stuff together. They can be removed with your fingers, assuming you have a mm or so of nail.
I could take pics but my SX is buried.
here's a pic I found, look on the lower left for a shiny black round object