“A Lockheed spokeswoman said the two parts are “very difficult to distinguish, visually.””
And apparently no one thought to put a little paint on one so they could tell the difference
If they’re worried about paint/coating on them maybe simply put each type of fastener in separate colored bins? Make it easy for the assembler to distinguish which was which? Maybe do a quick count (or weigh-in) at the end of each shift as a QA check that the right fasteners are being used at the expected rates...
I doubt that would make much difference to Bubba. I worked instruments in the Air Force. Right on the door for the compass transmitter was spray painted, "Use only non-ferrous fasteners". When a pilot would complain that the compass system was screwy, the first thing we'd check were those screws for the compass transmitter and many, many times the problem was because Bubba used the wrong screw(s).
Just another excuse for failure.