That may be true but it's not relevant to this accident. It was a British made plane using British standard screws. The mechanic just used the wrong size bolt from the same standard. It's not like he was trying to find a metric equivalent to an imperial size or vice versa.
According to the wiki, one of the recommendations from investigating body was that aircraft maintenance crews wear corrective lenses. Reading between the lines, it suggests that the tech didn’t either see the proper screw size or didn’t want to cross-reference with documentation because they couldn’t see the text.
