Used to be called Lin Bin Brackets. They are for hanging those little plastic trays you can buy from the likes of B&Q, Screwfix etc.
Very handy for screws, nails, washers etc
that is clever, better than lugging a big toolbox around the house for every little job, which I do. Well, I do now have dedicated electrical tool box, so that's progress!
I got rid of mine after spending lots of time on the floor getting screws and nails.
Somehow i always managed to knock them off the wall.
Now I use old tool boxes, all separators removed and keep screws and nails in their box.