I am so annoyed. I saw this thread the other day and didn't think anything of it. I spread 5 years of stone yesterday and lost the nut that holds the battery cover on my BX`1880. What is that nut?
Do you mean the black plastic knob holding the under-the-instrument-panel screen on?
It appears to be ¼" X 20 tpi, so it should be readily available. I might be metric, though. Maybe just check it with an ordinary nut to see. If metric you might have to order it from a dealer or someplace like McMaster Carr.