Just out of curiosity, what is the rational for the aircraft industry sticking with SAE?
Is SAE used on Airbus products? How about Rolls Royce engines?
O.K. Well technically, what we refer to as SAE, isn't! The original 'National' threads and bolt head sizes specified by the U.S. Society of Automotive Engineers were replaced in the 1950's by 'Unified' threads!
The threadforms and bolt head sizes were almost identical to the old U.S. National sizes, so nobody in the U.S. really noticed, and I suspect that the S.A.E. standards now reflect the change, but the aerospace industry worldwide would call these 'Unified'!
However... the whole idea behind 'Unified' threads was that the same sizes would be adopted by the U.S. Canada, and the United Kingdom, which it was, but it was a bigger change here!
Good idea though! 60 degree threads are easier to cut than 55 degree Whitworth and BSF threads, and the Unified system included threads in 1/32" increments for the aerospace industry! Everything was still measured in inches so no need for new equipment! Even today, some British made products that were originally made with British Standard bolts can be found with the Unified symbol of three interlocking rings to indicate Unified bolts have been used!
The British aerospace industry adopted Unified threads almost instantly, where they remain standard to this day, so every British airliner and military aircraft designed since the 1950's has unified fasteners! The same applies to Rolls Royce Engines (turbines certainly - think all piston engines are B.S.) The Rationale is that we have one standard that everybody is familiar with, so we stick with it! Aero engineers worldwide can service stuff with one set of tools, so job done!
Airbus is an unusual, but effective, amalgam of British and European firms. They seem to stick to the formula used to build Concorde, which is that the fasteners are normal Unified sizes, but with measurements in millimetres, for the hard of thinking!
Personally, my family has yet to get around to adopting these new fangled American threads and so I still work in British Standard! Metric is a long way off!!