I just looked at the picture again, I have seen them before, however here's an interesting one for you, the firm I served my time with used to make the cases for those boards!
We had a large press section and used to make some really strange things,we supplied steel for a well known firm that made filing cabinets, we produced parts for another well known firm that made gas cookers and fires, ( my uncle was in charge of r&d there), we made large flanges for wagon exhausts, and we even made the centres for cable drums.
Remember when cable drums were made of cardboard, and they had 3 curved pieces of steel that made the bit the cable wrapped around? Each piece of steel had 3 "fingers" that were bent over to hold the ends on the drum, well we made them by the thousand, as the apprentice, if we were not busy with electrical, they'd get me to jump on a machine if we were behind with the order.
Sometimes if I find an old drum under a floor on an older house, I'll look at it and think, "hmm, I wonder if I made this"?