Through the years I have amassed a lot of taps and dies of different thread forms and sizes. But despite this, it’s sometimes like I told my wife when she asked me what I kept in a certain cupboard. My answer was: Every possible threading tool, but the one I need at the moment!
Sometimes you have to compromise and use what’s at hand. From an engineering point of view 9/16”x20 could, for all practical reasons, be substituted with M14x1,25, wich is the most common spark plug thread. Then, of course, new nuts also have to be made, but they are commonly mangled too, in my experience. The difference is that the metric thread is about 0.3 mm smaller in diameter, and the pitch is about o.o2 mm finer. DO NOT MIX, even if it could be possible in one direction!
Yes, 9/16”x20 is one of the threads used for pedal cycle cranks, right hand on the right side and left hand on the left side, if my memory serves me right.