The bicycle industry takes from many sources the dimensional "standards" which we bike people deal with. These sources can be metric, ISO, fractional, Whitworth and others, sometimes within the same thread spec (like 10mm axles with 26TPI pitch). This is nothing new and one of the driving reasons Sutherlands started the wonderful manual decades ago.


To the OP's situation. The nuts look to be 9/16x18tpi. Most adult pedals and crank arms use 9/16x20tpi. Given the stress that pedal attachments see and the potential failures (and personal damage) that can (and do) result from pedals falling off cranks I STRONGLY do not suggest any attempt to chase/re tap these nuts. As it is the likely few actual threads of overlap is in it's self a concern, count how many threads are in action with a properly threaded in pedal. Think about the damage to how many threads before the pitches match back up. (close to a half inch by my rough math, which is close to how far a pedal threads into an arm). Then think how the through hole in the adaptor won't support the pedal axle, there not being anything but a clearance fit. So even more stability/support/securement is depending on the nut's ability to tighten down to a large enough degree.


When I read of this project a while ago I just shook my head. Now that I see the lack of homework/understanding about the simple factors at play, thread pitch, I am more worried. Andy.