[Arran]

Tim;
I noticed your post a little late, but I would take one of the junk sockets and try to break a chunk out of it with a hammer, or with a screwdriver blade. We all know how Bakelite breaks, with that rough texture, would they make a socket out of Teflon, I would guess not since phenolic resin is cheaper? If you can find some Soviet/Russian sockets, those would be good, I also remember seeing some from a Bulgarian seller of a different style where the ears were molded in, I have some similar ones to those made by Eby, but most of the Iron curtain stuff was either a copy of, or a derivative of something Western anyhow. Some other sockets that I was looking at once were some relay ones made by Omron, I think it was a seller in Taiwan, or Thailand wo was selling those.
Regards
Arran