At the top of our U-staircase in a house from the 1920s, there is a screw with a square washer (see picture). I would like to countersink this so that it's not visible, but before I touch it, I would like to know what its function is. It looks like a later repair or stabilization of some kind. Does anyone know?
/Oscar
/Oscar
Could be a previous repair, it looks like there is an old crack in the wagon frame a few centimeters below the screw, not exactly a discreet repair if so 
Okay. Should I dare to try unscrewing it, or is there a risk that the staircase will fall apart?
Remove it, if it gapes make a nice repair!